By now you’re probably wondering when this is ever going to end; we’ve made our models, turned them into molds…now what?
We fill them, that’s what. In this post I’ll discuss how to choose and layer frit into your mold, and getting them into the kiln. In the final post (next week), I’ll show you how we finished the panels.
For this post, though, you’ll do these steps:
- Prepping the mold
- Layering frit into the mold
Tools & supplies needed
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Turntable. By now this shouldn’t be a surprise. 😉 Putting your mold on a turntable helps ensure you get an even sifting of frit (when you’re looking for one, that is).
- Scales. Guesstimating the right amount of frit is easy once you’ve made a few of these but weighing is the sure thing, so scales are a good idea. If you’re building a series where the panels all need to be of similar thickness, they’re essential. I’ve made a couple dozen of these panels, but I can still be caught out (as you’ll see) in the next post.
- Water bottle with sprayer. If it’s the same one you used with the clay, clean it well–there should be NO clay residue anywhere because it has a nasty habit of slipping into your glass. If you’re not sure, get another one.
- Small dish or cup. It need only hold a few ounces of water, but it should be very clean; you’ll use it to dampen your brush and pick up frit.
- Scoop or tablespoon. For getting frit out of the jar, and for tamping it down. If you’ve got a set of measuring spoons, they’re great, but anything that scoops will do. (see also “Dental scoops,” below)
- Level. This is for ensuring that your mold is level in the kiln.
- A couple of empty jars with lids for mixing frit tints. I use empty frit jars (I have scads of them, and unfortunately the companies don’t take them back for recycling). The nice thing about frit jars is that you’ll have a lot of them too, once you start doing this, and they make excellent storage containers when you’ve made far too much of a frit tint.
- Sifters/sieves. Most glass places sell the funnel-shaped sifters and they’re good for delivering drifts of powder to a surface. If you’ve played with them awhile, you’ll learn just how much to overlap strokes to even things out. I use those, and the inexpensive flat-bottomed enameling sifters, which you can find online or in places that sell enameling supplies. I prefer the flat-bottoms for four reasons:
- They automatically deliver very even coverage without a lot of effort
- They come in three sizes, including a really tiny one that can deliver frit to very small sizes
- The twisted wire handle is actually a delivery mechanism, causing just enough vibration to deliver an even flow of powder
- That twisted handle can also be bent, making it easier to get the sifter into molds
- Brushes. Get new brushes that have never been used for anything else, and keep them in a pouch, away from your other brushes. Anything that gets into the brush can conceivably get into your glass. They don’t have to be expensive, but I’d get at least one of each shape:
- A flat, squared-off brush is great for making sharp edges in powder
- A flat, angled brush (you can buy a flat brush and trim it to shape) can push frit off edges and also make straight lines
- Two soft watercolor brushes, one maybe an inch long and the other very tiny, for pushing powder around in details
- A stiffer brush for clearing areas of frit–it’ll act like a broom
Tampers. You don’t really need them for this project, but if you’re interested in doing more pate de verre, make a couple of these. Go to the hardware store and buy the cheapest metal drawer knobs you can find. Get a round flat one, a square flat one, a curved one. Then buy a threaded rod that will fit into the screw holes of those knobs. (If they sell the rod in 6-8 inch pieces that’s ideal, otherwise, buy a longer one and hacksaw it into pieces when you get home). Screw the knobs on the rods, and you have wonderful tampers to pack frit into place.
- Dental scoops. I’m not sure how to describe these (right), but if you buy a pack of clay or dental tools, you’ll find that two or three actually have tiny spoon ends, or shallow depressions. Stick that end in a vise and bend it to about 70 degrees from the handle, and you have a wonderful tool for delivering small amounts of frit to exactly the right place, deep inside a mold.
- Sand. This is just plain old playsand or traction sand from the hardware store; a 25-lb sack will last forever. Mine is filled with mold crumbs, but still works fine.
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This is probably the hardest part of the whole project: What frits do you stick in this mold you’ve made?
Truly, anything goes. The simplicity of these panels lend themselves to just about any color combination you choose. Since this is a pate de verre exercise, we’ll use fine and powdered frit, but you could just as easily use a transparent billet…or a stack of scrap float glass. I’ve done both, and they’re stunning.
For pate de verre, however, let’s set a few ground rules before we go frit-shopping:
Set limits. Don’t throw in all the frit you can find; it’ll look muddy and busy and you won’t see much of the detail. These panels work best when you stick to one, two, or three main colors.
- You don’t have to copy nature. In fact, you probably shouldn’t. Get creative. Make your pine cones purple, or blue or…
- Plan on colors that layer well. Layering transparent colors in the same general area of the color wheel makes your piece look less like a coloring book and more organic. If you have one or two favorite colors of glass you like to work with, look for similar colors as part of your layering scheme. Most of my panels wind up using 8-10 jars of frit, but only two or three “visible” colors.
Stick to transparents. Pate de verre gets its beautiful, jade-like qualities from all the bubbles trapped in transparent glass, and layer after layer of colors viewed together. Opaque/opal glass stops too much light, and kills the effect. If you place it at the front of the panel, it will look painted.
- When can you choose opaque frits? I do use opaques sometimes, but in back, to stop the light in some areas and emphasize a color…or else I mix a very small amount into clear glass for a frit tint. For now, pick out transparent colors. (Hint: If you’re using Bullseye glass, the transparent frits have numbers in the 1000 to 1999 range. The opal colors range from 0001 to 0999.)
- Get out your reactivity charts. An unexpected color reaction can ruin your piece, so make sure you know what your frits react with. I’ve listed some resources in this post.
- Rely on the glass catalogs. The colors in a frit jar are usually MUCH lighter than the real glass, so it’s a good idea to keep your manufacturer’s glass catalog (or website) handy when you’re selecting colors.
- Shoot your jars. As we did with our frit selections, photograph your jars once you’ve gathered them on your worktable. It’s a fast way to document the colors and styles of frit that went into your piece.
Prepping for filling
Since we’d cleaned the molds during the moldmaking process, they didn’t need a lot of additional prep before filling. The prep we did, though, was critical:
- We made sure the glass had a clear path to all parts of the mold (if you’re not sure what this means, check Part II of this series under “mold engineering.”)
- We ensured that there were no fragile or jagged bits of plaster that might fall into the mold
- We removed all visible signs of clay bits, mold scrapings, and loosened plant material from mold crevices
- We dampened paper towels and (carefully) dabbed them inside the mold, picking up any dust or crumbs we couldn’t see. We also stuck a couple of dampened cotton swabs in deeper crevices, making sure the mold was completely empty.
When that was done, we weighed our molds. It can be tough to understand how much frit to put in the mold by eye; you’re liable to under- (or over-) fill. Here’s why:
The volume of frit changes with particle size; what doesn’t change is the weight. So if we know that a 5×7 inch pate de verre garden panel weighs between 600-800 grams, depending on how much you leave to trim off and the thickness (9 to 16 mm for these), then we can weigh our empty molds, and add maybe 700 grams. Then we keep filling the mold until it weighs the right amount.
If you’re making a different size, you can calculate the rough weight of glass needed by figuring out its volume:
- 1 cubic inch of soda lime glass weighs about 40 grams
- Roughly measure your piece (without the relief) and take the volume: If it’s 10 x 10 x 0.5 inches, it’s got a total volume of 50 cubic inches.
- 50 cubic inches * 40 grams per cubic inch = 2000 grams total, or about 4.4 lbs of glass
This is for soda lime glass, with a density of 2.55, including Bullseye, Uroboros, and Spectrum fusibles. Other types of glass, such as lead crystal, can have different specific gravities (Gaffer lead crystal, for example, is 3.6), so you’ll need to adjust accordingly.
Paul Tarlow has a little casting calculator that figures out casting glass weights for a particular volume. It’s a useful tool.
Weigh your mold right before you fill it. Molds contain evaporating water, the longer your mold sits, the lighter it will become (unless you take steps to trap the water). If you weigh the mold two days before you actually start filling, your mold will be lighter and you’ll add too much glass.
Back at class, we now knew the weights for mold+glass, so we set our molds up on the turntables, and selected our frit.
Planning your layers
The Bullseye+Uroboros 90 frit color palette is ginormous, one of the primary reasons I use it (besides the fact that they’re local companies and I’ve got an enormous stash of the stuff). By combining frits, you can literally make just about any color you could blend with paint.
On the other hand, ginormous choices aren’t always a great thing, especially if you’ve only got ONE mold to fill.
I’m often tempted to give up and stick with a single color, relying on the texture and design to carry the piece. That’s what I did with the red panel at right. There are actually about eight different frit colors in that piece, but they’re closely related reds, oranges and ambers, layered beside and over each other. They lend a lot more depth than a simple, solid color.
Carla loves green, and she wanted the same effect, only in greens. For her frits she selected jades, aventurine greens, turquoises, blues and a purple.
You don’t really have to worry about placing the color in the mold with this style. About all I do with these is rub a tiny amount of powder, in a contrasting color, into the deepest parts of the detail. You shouldn’t be able to distinguish it in the finished piece, but it gives just enough contrast to increase the highlights and shadows.
If you’re painting colors into specific parts of the mold, as Shelby and I were, it can be helpful to refer to a photo of the model. Shelby decided to fill the leaves with the yellow tints, add green for the thin stems connecting them, and put drifts of different greys in back.
I chose darker purples for the chestnut pods, shading to paler blues in the center. I wanted dramatic shading, dark at one end, light at the other, so I chose Midnight Blue and Sky Blue.
These pieces are mostly background, so think carefully about the result you’re looking for. Do you want the appearance of a solid background? Would you like the look of old leather? Would you rather have subtly mottled colors, like the forest floor in dappled sunlight? Or do you want bold, clashing stripes? Should the background contrast sharply with the detail?
We checked colors for reactive potential. If we’d wanted to use reactive colors, say, a yellow with a turquoise (sulfur in the yellow reacts with the copper in the turquoise to form brown), we’d need to separate those colors with a thin layer of clear powder, to prevent them from touching. (So we’d add clear powder to our list)
Colors selected, we roughly ordered our jars from lightest to darkest, to keep them straight. We’d put the darkest colors farther back in our background layers; if they’re in front, they’ll tend to mask the colors in back.
Layering frit into the mold
Start by laying out your frit jars, your brushes, a paper towel or rag, and cup of water around the mold. Reserve one brush as your “pickup” brush to pull frit out of the mold. The other brushes are best kept dry and clean; they’ll be used to neaten up expanses of frit.
If you’re coloring the relief detail, begin by sifting powder–fine or larger frit will make a grainier surface with less detail–into the deepest parts of the mold first, then gradually expand your fill areas as the frit levels rise.
If the area you’re trying to fill is too narrow, use a small scoop to deliver frit to the spot. If you accidentally spill frit into an unwanted area, get your pickup brush slightly damp with clean water (I squeeze mine out with my fingers), then touch it to the frit.
The frit will stick to the brush, and you can pull it away. Dip the brush into your cup of water, and the frit will fall to the bottom. Squeeze out the brush, and go back to your frit, until the area is clean.
Apply color the way you would to a coloring book; literally lay the color into the area, tamp it down lightly to compact it. Then apply the next layer, and keep going until there’s a mound of frit filling the depression and a bit higher.
Remember that the powder will compact down, so that the frit behind it will move into the relief areas. If the background is a contrasting color, you may see that in the detail.
That’s what Shelby did with her mold; then she used a tamper to pack it into the crevices (left).
Carla laid down various green powders the deepest areas of her mold, the lily pods. Then she slipped chunks of coarse Emerald Green frit into the center of each sphere. They’d provide a transparent glint, and let in a little more light.
Since I couldn’t remove the chestnut pods without damaging the mold; I kept things simple: I laid dark powders directly on the pods themselves, to fall to the bottom of the mold as the plant material vaporized, and outline the detail. The background frit would fall into the empty spaces and fill in the rest.
Filling in the background
Once the detail is filled in, you can start adding background colors, and there are lots of techniques for doing it. The easiest is to simply open the jar, dump it into your sieve, and apply it to the mold. You’ll get a layer of pure, transparent color (with millions of tiny bubbles), like solid powder color sample at right.
You can mix two or more colors of powder together directly; just dump them both into a clean, empty jar, close the lid, and shake like crazy. Then sift on. If you’ve used colors of approximately the same value, you’ll get a nice new “mixed powder” color, left.
Or you can “drift” your colors. Scoop a little powder into a jeweler’s scoop or spoon, and broadcast it gently across the mold. It’ll usually land in diagonal lines; keep doing that, leaving spaces between the lines, until you’ve used all the powder. Then pick up another color, and broadcast it into some of those spaces…and so on.
What you’ll get is a mix of shades that can be very subtle or extremely bold, like the “drifted powder application” at right. If you intersperse larger frit particles in the powder, you’ll get little transparent “windows” of color that can be striking.
You can “splotch” (fancy technical term…). Get a sun-dappled or granitic effect by sifting some areas, drifting others, and then just dumping small spoonful of powder here and there, as in the “splotched powder” example at left.
Frit tints. Once you’ve laid down at least 3mm of powder, begin to experiment with frit tints. They’re usually lighter and more transparent than straight powder applications because they’re essentially a thin layer of color around a bigger piece of pale fine/medium frit.
To make a frit tint, dump some transparent fine frit into a jar; I prefer a watery/crystal clear transparent because it doesn’t impart its own color. Make sure the jar is filled no more than half the way (the fuller the jar, the harder it is to mix effectively). Mist water over the frit with your schpritzer, close the lid and shake vigorously.
What you’ve done is coat the frit particles with a film of water. Now open the jar, sift in a colored powder, close the lid and shake like crazy. The powder will stick to the water filming the frit, and when fired create a “bubble” of transparent surrounded by color(s). (Bullseye has a nice article about frit tinting)
You can drift frit tints for a beautiful, watery effect, or you can simply layer them into the mold and tamp down. Or you can use different base glasses (the fine, transparent frit) instead of transparent. The example at right is actually a mix of BE Marigold Yellow and Marigold powder on Coral Orange Tint fine frit.
As the frit level rises, you can increase the frit size, to create larger, more transparent areas that make subtle background shadings, and let more light into the piece. . We added big chunks of blue and turquoise to my mold near the end of the fill; they’ll translate into dapples of color, deep in the background.
When your frit fill is nearly an inch deep, weigh it, and see how much more you have to go. Unless your colors are very light, you’ll want to concentrate on letting light into the piece with larger, coarse clear glass, or even clear sheet from your scrap bin.
Firing the molds
DO NOT PUT MOLDS DIRECTLY ON A KILNSHELF! (I’ve lost a couple of kiln shelves that way). I remove the shelves from the kiln and add about an inch of sand to the bottom. This lets me easily level the mold in the kiln and enables air to get under the mold for more even heating. Use the level to ensure that the mold is level; add a little more sand or remove some until it is.
Once you’ve arranged your molds, write down the schedule you’re using in big black letters on a piece of paper, and stick it in the kiln. Photograph the schedule, the pieces and they way they’re arranged in the kiln. It can be invaluable later on.
Then close the lid, propping the lid open by an inch or two, using a firebrick. Venting allows the residual water in the mold to escape without harming the glass or (much) the kiln. When the kiln reaches 1100F, I close things up. By then all the water has evaporated, and the most obnoxious vapors have escaped from the kiln.
This is the schedule we used. As always, your mileage WILL vary; this is only what works for me, in my old, worn-out kiln. Test this program a time or two (and adjust it) before using trying it with production work.
I’ve been caught out a couple of times with a too-short drying schedule (Segment 1), so I tend to hold the mold for steamout probably longer than I should. As I’ll discuss in the next post, I think I’d add an hour to the process temp, to ensure better rendition of very fine detail, too.
|1||400||250f/121c||12||Drying the mold|
|2||150||1100f/593c||1||Slow ramp; hold to remove chemical water|
|3||200||1490f/810c||2||Process temp (this time, anyway)|
Next post: The finish