Stained Glass Panels
Should zinc came be stretched like lead came?
If you can stretch zinc came, take up Olympic arm wrestling. You would be a sure winner!
Zinc came is actually a zinc-coated steel. Zinc is a soft metal with properties similar to lead. By itself, it has no advantages over lead. Steel is rigid and has way more strength than lead. However, solder will not bond with steel. But solder will bond with zinc, and zinc will bond to steel.
When you cut zinc came, take care not to scratch the zinc plating off the steel core where you need to solder a joint. Solder will only bond with the zinc plating. It will not bond to bare steel.
If you scratch through the zinc coating, the exposed steel will rust if exposed to the environment. So take moderate care in storing and handling your zinc came. If you do get a scratch or nick, you can cover it with a thin solder bridge, so the steel is not exposed.
I want to use Spectrum’s Baroque for the background in a panel. What is the best way to use this richly textured glass?
Picture in your mind a single, unbroken sheet of Baroque with the central design, just laid on top of it. Can you see the continuity of the swirls in the Baroque flowing behind and through the rest of the design? The effect is very pleasing and leads the eye around and through the central composition. It is one of the best uses of Baroque as a background glass. It will take your design from “very nice” to “wow!”
How do you go about accomplishing this? Do you just try to imagine what that large background sheet of glass would look like under your design and find pieces in your glass inventory that look like they "match"? Or do you somehow actually cut the glass pieces out of one big sheet of Baroque glass to get the continuation of the swirls?
Yes, and yes. The simple answer is that you take whatever approach works. That is simple to say, but it is difficult to accomplish.
If the panel is small enough, you can cut the background from a single large sheet. I think I would start by putting a few reference marks with my grease pencil on the glass. Then I would put my background pattern pieces on the glass and cut them out. You can probably see that your scrap factor will be 100% or more with this technique.
If you break a piece when cutting, you will have to find another piece with lines that match those of the broken piece as closely as possible. The farther the separation between pieces of baroque by intervening design elements, the easier it is to get a visual match. Adjacent pieces of baroque can be difficult to match when they come from different sheets of glass, or from different areas of the same sheet.
The key to this technique is the visual flow of the lines in the glass across the entire background of the panel. When the background cannot be cut from a single sheet, you just have to eyeball it.
The process begins when you buy your glass. Try to select sheets that have similarity in the swirls in terms of spacing, curve radius, color intensity, etc. If you have to ask your local retailer to special order what you need because their selection is limited, or if you mail order this glass, communicate clearly what you are trying to do. Almost all of the warehouses are quite willing to sort through a crate of glass to select the two or three sheets that you would select if you were there. They want happy customers and repeat business. They will do their best to assist you, but you have to make them clearly understand what you are doing, and what you need. You should plan on buying 2 to 3 times the area of glass that you actually plan to use, when you cannot cut from a single sheet.
When you get your glass, spend time to study it. Visualize areas of it in your design. Mark areas with your grease pencil as your visualization firms up. Try to cut adjacent pieces in your design from the same area of one sheet. Try to limit your discontinuities in texture to areas widely separated by intervening design elements. For example, you have lines in the glass that become tightly bunched as they dive into other elements of your design. The closest match you have in the next sheet of glass is some bunching, but other lines that are more widely spaced and diverging. If you have several inches of intervening design elements, this will work quite well. The "eye" will see a convergence and hidden divergence in the flow of the lines.
Small angle divergence or change in direction can be handled the same way. If your eye flows through the design, following all of the dips and turns without interruption, then you have succeeded.
A truly exceptional piece of work would not only maintain the continuity of the texture, but would use the texture to draw the eye into the principle design. That type of work requires a high degree of talent and skill, and a "jackpot" level of luck to find the perfect glass.
How do I cut lead with long narrow angles, and what is the best way to cut joints where three lines come together?
Very long, very narrow tips on the came are a challenging skill level to cut. I have seen a master do it with a lead knife on 3mm came, so I know it is possible. I am not sure I could do it. One thing he did do to make this cut was to wipe his knife on a block of paraffin. He explained that this lubricated the blade. Without it, such cuts would not be possible. Make sure the blade is sharp, and lubricate it. The second thing the master did was to use a side-to-side wiggling motion, not the back and forth rocking motion that practically all of us have been taught in cutting lead. His explanation was that the rocking motion on long sliver cuts would crush the face and ruin the cut. The side-to-side wiggling motion is what makes such cuts possible.
You can try those suggestions. If you still have trouble, you may want to try a less severe angle cut by cutting the intersecting piece of lead differently. In either case you will probably have to remove some of the lead heart. The master did not use lead nippers to remove the heart. He held the came, face up, on the edge of the table, held his knife on its side, and with that same side-to-side wiggling motion neatly sliced the face from the heart, top and bottom. Then he picked up the came, bent the separated heart outward, and sliced it off with the knife. Before each and every cut he made, he wiped the blade of the knife on that block of paraffin to lubricate it.
A common technique among those of us with developing skills and still in awe of the masters is to nip out a short length of the lead heart, and then use the lead nippers to cut each face of the came to the angle desired. This is simple, and it works.
Where three or more lead lines meet, dividing the intersecting angle equally between the cames makes the neatest strongest joint. Always cut the most difficult angles first, before cutting the other end of the came to length. Lay the lead on the glass at the angle it will come in at. Eyeball half that angle with your lead knife on top of the came. When you are satisfied that the blade of the knife is in line with the center of that angle, scratch the face of the came to mark it with the knife. Mark the angle with the came on the other side of the one you just marked. Now take your came out on the table and cut to the marks you just made.
Draw 3 intersecting lines 120 degrees apart. These lines represent your lead came. Now extend each line through the intersection for a few mm. These short lines would be the cut lines on your lead. You can see that the cut angle on each side is 60 degrees, exactly half the angle of the intersection of the cames. Now try some random angles between three lines, extend them through the point of intersection, and study the cut angles. You will quickly understand what I tried to describe above.
In some cases, usually very small angles, you may have to remove a little bit of the heart to get everything to fit together just right.
I want to use jewels as stars in a night sky, but I don’t want all those cut lines. Can I drill holes in the glass for the jewels?
Why not? I've thought about this technique to drop a jewel in the middle of a piece, but I have to admit that I have not done it. But I see no reason why it would not be possible. My thoughts for what they are worth on how to do it: I would place the jewel on the glass and trace around it. Then drill a 1/4" hole within the boundary. Get out the grinder and enlarge the hole. Foil the inside edge of the hole and foil the edge of the jewel. Drop the jewel in the hole and solder.
Keep in mind that the process is delicate, and you can easily break the glass at each stage of the process. Use a diamond drill with water. Build a little dam with putty to hold the water where you are going to drill. Let the drill do the work. Go slow with very light pressure on the drill. Do it on a drill press with a board to back the glass.
Do the same with the grinder. Don't force it. Go slow and let the grinder bit do the cutting. With a 1/4" hole you may start with a 1/8" grinder bit. As the hole gets larger, stop and change to a larger grinder bit. And keep the water flowing. You have to remove the heat, or the glass will break.
When you solder, watch your temperature. Don't dwell in one place and keep the tip moving. If you apply heat too long in one place, the glass will break. Think about it. The glass is trying to expand with the heat, and it has nowhere to go, since you are out in the middle of it. The only way to relieve the expansion stress is to crack from the hole out to the edge.
I didn't say it would be easy. I only said it is possible.
What texture of putty do you use when you cement a panel?
If the cement is too thick, it will be difficult to work into all the voids between glass and lead. If it is too thin, it may dribble out the backside and fail to fill the voids. You want a consistency in between. Trying to describe that, or giving a cookbook formulation is difficult. Some have tried to describe it as cold honey.
One of my instructors taught it this way. When you wipe your cement from the glass into the came, you want a little bit to squeeze out on the backside of the panel. If it is not squeezing through in some places, then it is too thick. Thin it until it does squeeze through, but don't thin it more than that.
This trial and error method will get you to the right consistency. With more experience, you will know this consistency, and will no longer have to experiment to get it right.
How tightly should my glass fit the lead came?
Ideally, there would be no slack. Everything would fit together like it was precision machined, no gaps, no bulges. Someday when we all have laser cutters on CNC machines.... Until then, we do the best we can. Sometimes, we can get a little point on the glass to dent into the soft lead heart without breaking the glass while tapping it in, but I think picking up the grozers is easier and less risky. Pieces that are just cut too big will have to be grozed or ground down to fit. There is no way around that one.
Slightly undersized pieces, or "poorly cut" pieces that leave a gap between the edge of the glass and the lead heart are OK if the edge of the glass is covered by the face of the came. These are the "loose" pieces in an assembly. If you do a good job of cementing, the cement will fill these gaps and the final panel will be tight and weatherproof. Obviously, if the face of the came does not cover the edge of the glass, that piece will have to be re-cut so it fits better. Otherwise you would have a hole in your window.
Work to your pattern. Get reasonably close. Don't get sloppy. But don't get hung up on precision either.
Do I have to cement my panel? Can I use silicon caulk?
Lead came construction requires cement. The panel will not last very many years if it is not cemented. It will sag and fall apart, even if weatherproofing is not necessary. Copper foil construction does not require cement, because the foil is burnished tightly against the glass and held in place by solder, which seals all the gaps between pieces.
There is a proper cement, and it is hard after it cures. The primary purpose of the cement is to seal the panel against the weather. You don't want water coming through and running down on your floor. The secondary purpose of the cement is to add some structural integrity to the panel. Without it, things would bend and sag very easily. I'm not sure a soft cement, like silicon rubber, would provide this
same structural integrity, although it certainly would weatherproof the panel. The third purpose of cement is to cover the sins of loose fitting glass in the lead latticework although we don't often admit this third reason.
There are formulas for cement published in various books, and on internet websites if your want to mix your own. All stained glass suppliers carry a ready mix if you want to go that route. It is more convenient. If you do a lot of production, mixing
your own may be more cost effective.
What are hinges and weaving?
Think of a panel made up of squares. Now envision the continuous length of lead running horizontally across the center, from side to side. The vertical lead lines are cut and soldered to a continuous horizontal piece. This continuous horizontal length of lead is a "hinge". The weight of glass above and wind buffeting the window over time will cause the lead heart, which is only 1/16-inch thick and has little strength, to bend and buckle out.
Think of the same panel, but this time the horizontal lead runs the length of two squares where it intersects the center of a vertical length of lead, which runs the length of two squares. Thus, the vertical and horizontal lengths span no more than two squares. Each vertical length ends in the center of a horizontal length and visa
versa. This is "weaving".
If you ever get a chance to see a 200 - 300 year old "diamond" window, this weaving pattern in the lead is exactly what you will find. If long continuous lead lengths had been used in its construction, it would have buckled along these hinges and fallen apart long ago. Yes it seems like a little thing, but it really is the difference between a 30-year window and a 300-year window, all other things being done correctly.
I used squares and diamonds for illustration here, but the same practice of "weaving" to break up "hinges" applies equally to any design. If you look at many, many designs, you will also see that long continuous lead lines are generally avoided. Break up the design. Even with lead weaving, a continuous lead line can form a hinge point. It is a structural weakness, subject to eventual failure. "Weave" the glass also. This is why you will see offsets in rectangular border pieces from the field pieces.
I don't know that there is a "safe" continuous lead length. Some designs have larger pieces of glass with long runs of lead that are OK. Just break up your lead runs and "weave" them where you can. In symmetrical designs, be sure your lead runs on one side match the lead runs on the other. Believe me, if they are different, it will show through and detract from the appearance of an otherwise magnificent composition.
What is a scythe stone, and how is it used?
A scythe stone is a hand-grinding tool, used much like a file to remove sharp slivers from the edge of a cut. It is also called a carborundum stone. It is about 1.5 inches wide, 10 inches or so long, ˝ to 1 inch thick with curved or flat surfaces, depending on the manufacturer. It is made of silicon carbide particles (carborundum is a registered trade name for one manufacturer of silicon carbide). The silicon carbide particles are held together with a waterproof resin binder. It leaves a rough surface like a coarse grinder.
Yes, you can accomplish the same thing with grozing pliers, or a powered grinder. The stone is just another hand tool, preferred by some, shunned by others. It is not an essential tool. It does leave some very minor chipping along the edge of the glass when used, much like the grozing pliers.
Most stained glass suppliers carry these stones. The next time you go to the store, look for one. See it, feel it, and ask the shopkeeper about its use. Whether you adopt its use or not, at least you will know more about it.
You can use the stone wet or dry. Using it dry will generate glass dust that you don't want to breathe a lot of over an extended period of time. With dry use the stone will clog with glass particles and its cutting efficiency will be reduced. If you use it dry, clean the stone by washing it, or brushing it with a nylon scrubbing brush when it gets clogged. The binder used to hold together the silicon carbide particles in a stone is impervious to water. Not only will the use of water keep glass dust under control, it will act as a lubricant to wash glass particles out of the recesses between silicon carbide particles in the stone. Reducing clogging of the stone will keep it "sharper" and it will cut more efficiently. Heat buildup is not a concern in hand use of stones, as it is in a grinder. The slower motion of hand use, and the time between strokes allows the heat generated in the glass to dissipate. So, yes, get messy and use water without fear. You can also add a drop of liquid dish detergent to your water. This will greatly improve "wetting", which will result in better dust control and cleansing of the stone
Should I use pushpins or horseshoe nails to assemble my panels?
I use the stained glass pushpins, although they are more expensive than the office supply store pushpins. All I can find at the office supply store have plastic heads and a 3/8" pin. The SG suppliers sell an aluminum head with 5/8" pin. The longer pin has better holding power, and the aluminum headed pins will last the rest of my lifetime.
Horseshoe nails were originally used when the panel was assembled on a plank of wood. Back then, old growth trees and planks up to 4 feet wide from them were readily available. Horseshoe nails were the staple hardware of the day. Pushpins were not yet invented. Many artisans still use the traditional horseshoe nail, but on plywood or some type of fiberboard today. There is nothing wrong with this method or materials. Either pins or horseshoe nails will work quite well. The choice usually stems from what you were taught with from your first teacher. You learn a particular set of tools and methods, become comfortable with them, and tend to stay with them.
Never use the pin or nail directly against the glass or lead came in your project. If you are holding lead in place, use a small piece of scrap glass in the lead with the pin or nail against the scrap of glass. A chip in the scrap piece won't matter and your lead will get no scratches or dents.
If you are holding glass in place, use a small scrap of lead came against the glass, and pin or nail next to the lead scrap. By using scrap lead, the glass will be held at the same elevation as the pieces already leaded, and the holding force is in the plane of the glass, against the lead heart. This helps keep things tight and avoids bending the lead came out of the plane of the panel. If you pin unsupported glass, aside from the possibility of chipping it, the unsupported edge can drop down onto your lay-up board. This can pry open the lead channel it is seated in causing a loose fit. It also puts an upward force on the assembled pieces, which can make a wavy panel. Do it right, and it will be flat and tight.
I have heard claims that the wider horseshoe nail provides more support, but I have not had any problems with pushpins (which is what I was taught with by my first teacher). I find pins easier to use (I don't have to hammer them in), and they hold the glass and/or lead in place without shifting.
What is under the pins should be considered as well. A good deal of my success is probably due to my lay-up board underneath. I have a series of lay-up boards that have collected over time as I make different sized panels. My smallest board is 20"x30", and my largest is 48"x60", with several in between. I use 1/2" birch plywood for the base, which I cut with a skill saw from 4'x8' sheets. I then cut a piece of "sound deadening" board with a utility knife to fit the plywood base. The sound deadening board is a medium density fiberboard, 1/2" thick, available from home supply centers in 4'x8' sheets. It is a dark brown color and reeks of creosote fresh from the pile. I leave it outside for a week and the aroma completely dissipates, so I can bring it into the shop.
I cut two pieces of 1/8" thick, 3/4" width aluminum angle iron to length and drill oversized holes in one side for #10 pan-head wood screws in a 3/4" length. With a framing square, I attach the angle irons along two edges of the lay-up board, on top of the fiberboard. I then put a few 3/4" lath screws (these have a very wide, very thin, flat head) along the other two edges to attach the fiberboard to the plywood. Aluminum bends quite easily, and I find the thicker, wider angle iron to keep its straight lines, and not be too heavy.
The 5/8" push pins hold very well in the sound deadening board, even when I hit a pinhole from a previous assembly.
I have two coffee cans; one with short lead came scraps, and one with short narrow pieces of scrap glass, for assembly. To hold a piece of glass in place, I put a scrap piece of lead came on the edge of the glass with the pushpin against the lead. This prevents chipping the glass and holds it in line with the rest of the assembly. To hold a strip of lead came in place, I put a piece of scrap glass in the channel with the pushpin against the glass. This prevents nicking the came and holds it in proper alignment to the rest of the assembly.
One thing I have learned over the years is that good tools make the expression of your craft a lot easier. Fighting with poor quality or inadequate tools makes the task much more difficult and makes achievement of high quality work almost impossible. Having the right tool for the right job makes work a pleasure. Invest wisely in the tools of your trade.
Can I use 40/60 plumbing solder on my panels?
If you can find a solder properties chart on one of the solder manufacturer's sites showing melting temps & pasty range from 100% tin to 100% lead with all proportions in between, it will help your understanding, selection, and use of solder.
The chart will appear as a broad "V" with the lowest melting temp offset towards Tin at a proportion of 63%tin/37%lead. That is called "eutectic" solder. If the chart shows the pasty range, it will be a broader "V" under the melting point "V". At the eutectic point, 63/37, there is no pasty range. In other words, eutectic solder transitions from liquid to solid all at once as it cools. At other proportions of tin/lead there is a range of temperatures where solder is partially solid and partially liquid, hence the description "pasty".
The Tin side of the chart has higher melting temperatures than the Lead side. If you use the 40/60 plumbing solder, I think the melting and working temperatures put you very near the melting temperature of your lead came. Also, since you have to have a higher temperature at the tip of your soldering iron, you risk breaking your glass from thermal stresses. If you use 40/60 on foil projects, you need to be an expert in soldering techniques to be successful in not breaking your glass from thermal shock. That is probably why we don't use 40/60 as a general rule. We are probably better off leaving 40/60 uses to the plumbers and their copper pipes.
Eutectic solder is the most expensive solder. The properties of 60/40 are very close to 63/37, and 60/40 is much cheaper. 63/37 does have its use in decorative soldering, since it has no pasty range. It can be applied over 60/40 without affecting the 60/40 bead if you are skilled. The surface of the 60/40 will become pasty under the 63/37 applications so you will get good adhesion of the decorative touches to the underlying 60/40 beads.
50/50 has a higher melting temperature and larger pasty range than 60/40. You can apply 60/40 over 50/50 the same way I described 63/37 over 60/40.
So is one better than another. No. For 90% of our work, it really doesn't matter. It becomes a personal choice of what you are used to working with. In changing from one to another, you have to readjust the soldering iron temperature and your techniques a little to get the same result.
I use 60/40 for most of my work. In foil work, I use 50/50 to fill gaps, and then make my bead with 60/40 over the 50/50. This prevents the solder from flowing through the gaps. I use 60/40 on all of my lead came work to minimize the risk of melting the lead came if I should linger too long on a joint with the iron. I think 60/40 gives me more working time than I would have with 50/50 and higher temperatures. Of course, if I were an "expert", I wouldn't be worried about such things.
Can I touch up my solder joints, and how do I remove excess solder?
Don't be afraid to touch up a solder joint that is just not right. Yes, you can melt the lead came, or crack a piece of glass if you apply too much heat to a joint. Let a bad joint cool for a few minutes, add some flux, then run your soldering iron over it again to smooth it out. If it needs more solder, add some. If you pull the iron away while the flux is still active, the solder will smooth right out. If you have too little flux, the solder tends to pull away with the iron and form peaks. Too much flux and it will splatter as it boils from the heat, and will add to your clean-up job. There is a point of just the right amount of flux, the right amount of solder, and the right amount of heat for just the right period of time, that will give you the perfect joint. When you have soldered a few hundred joints you will develop this skill. It takes practice. There is no other way to learn this, except by doing it, over, and over, and over.
If you have too much solder on a joint there are two ways to remove some of it. (Well 3 ways, if you count using your lead nippers to nip off an ugly peak before you flux and reflow.) First, clean the tip of your soldering iron, flux the joint, and wipe it with your iron. The iron will pick up a small amount of solder. While you may be tempted to "flick" the iron to get rid of this solder, that is not a good practice, particularly when you are in shorts and sandals. Wipe the solder off the iron with a damp sponge or rag. Repeat this procedure as many times as necessary. This will remove excess solder from the surface, but it will not remove solder from within a joint if you are doing a repair, and wanting to disassemble the joint.
The second method is to "wick" the solder off, or out of a joint for disassembly. You can buy a product called "Solder Wick" for this purpose. It is braided fine copper wire coated with a dry flux. Flux the joint, lay the braid on, and put the tip of the soldering iron on the braid. Solder just "wicks" up the braid and is trapped between the copper wires. Slowly pulling a length of braid under the tip of the iron will clean a lot of solder out of a joint.
You can get Solder Wick from your local SG supplier. It is a bit costly for the short lengths you get in a little plastic spool. You can also find it at Electronic suppliers, but the kind used in electronic repair is coated with an organic rosin flux that requires alcohol cleaning. Stay away from the electronic solder wick. We use water-soluble fluxes in stained glass work.
At the electronics supplier, you can buy larger spools of copper braid. It is usually "tinned" copper braid. In other words, the fine copper wires have been coated with tin. It will be a silver metal color. It is used in electronics to sheath wiring as a signal shield, or for ground straps. If you flux this braid, it works just as well as the commercial solder wick, and is a whole lot cheaper.
This type of copper braid is what you find in TV coaxial "coax" cable. Strip off the outer insulation and there is the braid. Cut off a length, and slip the braid off the inner conductor, and you have a length of "solder wick". This braid may or may not be tinned copper, depending on the type and quality of coax cable. Use it as described above. Really cheap coax will have a looser weave than the better stuff (fewer copper wires in the braid), but it still does the job. You will just have to use a little more of the cheap stuff to wick up the same volume of solder.
How can I improve my glass cutting skills?
Knowing how to cut is the first step. There is a definite sequence, or order, in the cuts you make to produce a certain shape. You have to study a piece and plan the cutting sequence. You have to "know" the glass you are cutting. Some types of glass break differently than other types. Some are easy and some are difficult. Some glass is very hard, difficult to score, and breaks often take off on their own course. Other glass is as soft as butter, takes a very light touch to score, and breaks cleanly every time.
A good score is very important to a good break. There are three elements to getting a good score: the cutting tool, the glass, and the artist holding the cutting tool. The tool must be sharp, clean, and oiled. Replace the cutting wheel when it gets worn or nicked. Use carbide wheels rather than steel. Before each score wipe the cutting wheel to clear it of glass chips from the last score. I keep a rag in a tuna can soaked with cutting oil for this purpose. Even though I use a self-oiling cutter, I wipe it in the can before every score. Clean your glass. Dirt will interfere with your cutting wheel, put wear on it, and may cause minute skips in your score, which will allow the break to run off the score line. I use a little Windex and paper towel to clean each sheet of glass before I start cutting. And finally, keep the cutting wheel perpendicular to the glass. If you lean it left or right going around a curve, your break will lean left or right through the cross section of the glass, and has a much
higher probability of taking off on its own. I position my glass and go through an "air cut" before I put the cutter on the glass. This helps me get positioned so my hand can maintain the perpendicular relationship through the entire cut. And you also have to maintain an even pressure, appropriate to the hardness or softness of the glass being cut, on the cutter throughout the score. Position and pressure are the training you have to give to your muscles. The knowledge plus the muscle conditioning are what we call skill.
The speed with which you score is irrelevant. Speed will come with skill, but I would ignore that aspect of it. Focus on pressure and position in scoring. I have scored some difficult shapes at a snail's pace and gotten clean breaks. And I've zipped straight-line cuts in Cathedral with clean breaks. (I won't dwell on all the bad breaks I have had, but I will say that most of them occurred when I did not follow the guidelines I have laid out above.)
Think and do. Think and do. There is no substitute for practice in developing cutting skills.
Can I use DAP glaziers putty, or should I use a stained glass pre-mix cement when I cement my leaded glass panels?
Dap 33 is pretty much the industry standard glazier's putty. A lot of artists use it for SG work. It can be thinned with turpentine or mineral spirits to get the working consistency you want. You can also add artists pigment to color it. Or, you can add the traditional lamp black to shade it in tones of gray to black. If you get it a little too thin, you can add whiting powder to thicken it up.
Most SG suppliers carry "cement" specifically formulated to the stained glass industry. It is white, gray, or black (Dap 33 is a slightly pinkish color), and is much thinner than Dap's putty. The basic difference between the two is viscosity. Dap is stiffer so that a bead of it stays in the window frame without sagging. SG cement is thinner so it will squeeze into all the crevices around the edge of the glass in lead came. Both Dap Glazier's Putty and the SG cements have the same basic formulation: whiting powder (which is calcium carbonate, commonly called "chalk") used as the filler to provide bulk, turpentine used as the vehicle to control viscosity (it evaporates quickly), and boiled linseed oil used as the binder to hold the powder together and adhere to the "frame" to provide the weather tight seal. Boiled linseed oil, when exposed to oxygen in the air, "polymerizes". That is, the short molecular chains in the oil join together with the oxygen molecules to form long complex molecular chains. This is what gives it the binding and adhesion qualities. Obviously, the surface polymerizes first as the turpentine evaporates. This polymerized surface film slows the rate of turpentine evaporation, and oxygen penetration for further polymerization. Thus, the rate of cure is exponential. Most of the curing takes place in the first 24 hours, but the process continues for weeks or months. Eventually, UV, other contaminates, hot-cold cycles, etc., will attack and break down the polymerized molecular chains and the putty (or cement) will degrade. This is why windows have to be re-glazed periodically, and SG panels have to be restored every century or so.
The formulation of SG cement is centuries old. In addition to the three basic ingredients, which I described above, lamp black (the carbon deposits that precipitate on kerosene lamp chimneys when the flame is not adjusted properly) is the next most commonly added ingredient, used to color the cement. Lead came develops a black patina as it ages, so black cement goes very well with it. It basically "hides" the cement from the eye. But there are times when a white or gray cement color may be more appropriate. In some cases, white might have a better appearance with mirrors or dichroic glass. Gray cement would be the best choice for use with the new lead-free cames, since they do not develop the black patina of lead cames, but maintain their shiny silver appearance.
The other ingredient that is sometimes added to SG cement formulations is plaster of paris. As you may know, plaster of paris dries to a very hard substance, without a lot of shrinkage. It is most commonly used for plaster mold casting because of these properties. When added to SG cement, it makes the cement harder, more durable, and somewhat enhances the mechanical structure of large panels. By itself, plaster of paris would be too brittle for SG use, but when used in proportion to whiting powder and boiled linseed oil, it produces a very tough, durable cement.
There are as many formulations of cement as there are books and manufacturers. The variations are very minor, and any of them may be used successfully. You can find formulas in books or with Internet searches. Many formulas have been re-published many times over, so you will probably find the same formula from several sources.
A large studio doing a lot of cementing will usually find it more economical to mix its own in a 5-gallon bucket. You can get whiting powder by the 50lb bag from distributors for this purpose. Small studios and "weekend warriors" usually find the pre-mixed cement from their local supplier to be much more convenient. I am a small shop and I use Inland's pre-mix in 1qt cans from my local supplier. Between panels, I usually find that I have a half-quart on the shelf. The whiting powder settles out to the bottom, and it takes at lot of stirring to get it mixed back in to an even consistency. My usage is going to have to grow considerably before I want to tackle stirring the 1-gal cans.
I just pour it out of the can onto the panel and work it into the came until it is squeezing out on the backside (that is how I know I have the right consistency). Then I squeegee off the excess and put it back in the can for reuse. I usually have to add a tablespoon or two of turpentine to the second half of the can to control my consistency (viscosity) and account for what has evaporated when working it on a panel. The last can of cement I bought was a little runny, so I had to add about 1/2 cup of whiting powder to thicken it up to the right consistency. A consistency of "cold honey" is about perfect.
I think the only time I would mix my own cement, was if I were doing a very large panel and wanted to use a plaster of paris formulation for a little added strength. Otherwise, I have had very good results in using the pre-mix products.
The Art of Soldering
Perfect soldering is an art in itself. Unfortunately, few artists master the art of soldering. The knowledge of soldering is fairly simple to acquire, but the skill takes a LOT of practice and time to develop.
The surface of copper (or lead) quickly oxidizes when exposed to air. Solder will not bond with this oxide layer. The purpose of flux is to strip off the oxide layer so bare metal is exposed to the molten solder and bonding can take place. Heat activates the flux at a temperature below the melting point of the solder. You can see this when you apply the iron and see the flux start to bubble and sizzle. If you apply a thin coat of paste flux to the face, it will not strip the oxides between pieces and solder will not flow into that space. A heavy application of paste flux may flow into the space when heated sufficiently and some solder may follow, but you cannot depend on this to get a good solder joint.
For proper solder flow and adhesion, all surfaces of the metal should be coated with flux. The popularity of liquid fluxes stems from the fact that it is easier to brush into the narrow spaces between pieces than are the gel or paste fluxes. The disadvantage is that liquid fluxes dry out and lose their effectiveness much quicker than gel or paste fluxes. Read that as less working time. The technique in using liquid flux is to coat a small area and solder immediately. Read that as a lot more back and forth between the flux brush and the soldering iron. Liquid, vs. gel, vs. paste flux is a trade off of how you want to work, difficulty of application versus more frequent application. The important point, regardless of which flux you choose, is to make sure all surfaces that you want solder to bond to are coated. You can apply insufficient flux (solder doesn't flow like it should), but you can never apply too much flux (just more mess to clean up). Since you have to clean the panel anyway, be liberal in applying the flux and you won't have a problem.
The real skill is in the application of heat with the soldering iron. You have to get all the surfaces hot enough for the solder to flow and bond. Too much heat and the solder flows right through. Still more heat and you temperature shock the glass and it cracks. There is no way words can give you the skill required. Only practice can develop the skill necessary.
The first thing is the temperature and thermal mass (heat capacity) of the iron. If the iron is too hot, you risk cracking the glass. You want a temperature of the iron that will quickly heat the surfaces to be soldered, but not over-stress the glass. When you put the iron on the surface to be soldered, heat flows from the iron to those surfaces. The flux and a little bit of solder helps conduct this heat. If you have a wimpy little iron and a large surface to be heated, all the heat is sucked out of the iron very quickly and you have to hold it there while the iron recovers. This is disaster in the making. Put that wimpy little 80W pencil iron you got with the SG starter kit on the shelf. Spend the $100 bucks it takes to get a decent Hakko or Hexagon 100W iron that has some "beef" to it. A larger, heavier iron has more thermal mass. That is, it holds more heat to transfer to the soldering surface and it won't be sucked dry.
Many wimpy-iron artists try to compensate for their deficient tool by running it at a higher temperature. This technique usually results in more cracked glass, and they still get run-through because the iron just doesn't have enough thermal mass, and they have to hold it in one place too long to get the solder to flow.
There is one other technique wimpy-iron artists employ, but it is twice the work, although it does yield good results - sometimes. Some use 50-50 solders to fill the spaces between pieces then form the bead on the face with 60-40. 50-50 has a higher melting temperature than 60-40 and so the run-through problem is lessened. However, the risk of cracked glass is much greater in the higher temperatures needed for 50-50, particularly with a wimpy iron set too hot to compensate for the lack of thermal mass.
Get yourself a decent tool, and you will be amazed at how much easier it is to solder.
The final skill is in keeping the iron moving and feeding the solder. When you can do this without run-through, without cracked glass, and without touch-up required, you have mastered the art of soldering. The right iron temperature and feed rate will accomplish this. It just takes a lot of practice. There is no other way to learn it.
When you do have to touch up a bead, don't do it while the bead is still hot. Invariably, you will get run-through if you attempt it. Let the joint cool, apply more flux, then run your iron back over the bead. Usually this is much quicker, since you only need to re-melt the bead, not the whole joint. Some leave touch-up to the end, set the iron to a slightly lower temperature, then touch-up the whole panel as a separate operation.
I used foil pattern shears to cut my pattern pieces, but when I finished the panel it had shrunk. What did I do wrong?
You did nothing wrong with the pattern shears. The pattern shears cut out 1/32" (0.03125"). Foil thickness is 0.0015", which will leave a space of 0.02825" between perfectly cut pieces. What you did was to "scrunch" all your pieces together during assembly, which eliminated that 0.028" spacing between them. The cumulative effect of scrunching was that you ended up 1/4" short in your finished panel. I'm sorry you came to grief, but you are not alone. This is a very common mistake. And there are a lot of teachers that should be taken to task for not teaching the ins and outs and whys of the foiling method.
That 0.028" space is for solder. The solder heart between pieces is extremely important for structural integrity. It is what gives rigidity to the panel to resist the forces of nature that cause a panel to bow. It provides support to the pieces, which resists the forces of gravity in causing a panel to sag. Without that solder "heart" you have only the face solder beads and the foil adhesive (which doesn't count for squat) to hold your panel together. The strength of a panel with no "heart" is less than half of that with one. If you want your work to last longer than you do, give it "heart".
So go pick up those pattern shears from wherever you threw them, and
use them with confidence. Now you know better.