Playing with glass blocks

>, studio practice>Playing with glass blocks

Fresh-from-the-kiln color samples (well, I coldworked them a bit) These are mostly earthtone pate de verre shades I’m testing for a client.

The reward for patiently, carefully weighing and mixing and packing frit into little plaster cells, then documenting the result? You get to play with blocks (right).

Those of you who’ve been to the studio know my obsession with color tests and frit mixtures. I have LOTS of these little things.

The cool thing about frit is that it can hide or show the true nature of the glass. In sheet or rod or cast form, black glass looks, well, black. Stretch it thiiiiiiiiin, though, or cut it with enough clear…and you get dark violet.

Baby-poop brown (NOT my term, a friend calls it that) makes one of the most beautiful clear saffrons, dark blues dilute to periwinkle, etc. And the only way you’re gonna know this stuff is to test it.

20090831-rcc134 of the samples in the above picture were made with about eight colors of frit. (The 35th, the little blue tile at bottom left, is a Gaffer lead crystal sample I needed to test for another project.)

I once tried to build a full catalog of readily available tints but it seemed to be a never-ending battle, and after awhile I just gave up.

It seemed as though every time I’d think I’d nailed one color of glass another permutation would pop into my brain. At 7K plus samples, I hadn’t even started the blues yet.

Finally, one day I sat down and figured out how many combinations I should test:

  • Total number of Bullseye glass frit colors: 109
  • Total number of Bullseye frit sizes available: 109 x 4 + 1 (Extra coarse clear) = 437
  • Standard frit tint test panel: 10 tints (0%, 1%, 5%, 10%, 15%, 20%, 25%, 50%, 75%, 100%)
  • Total number of standard BE single color frit tints possible: (437 X 10) ^ 108 = 1.5e+285

20090831-ncc5Uhm, that’s a really big number.

Bigger even than the US deficit. Add in all the possibilities from an additional 241 Uroboros 90 frits, and the calculators stop giving me numbers.

Let’s just call it “a whole bunch.”

Realistically, of course, not all these combinations will produce tints that can be distinguished by the human eye. Some of them will be splotch-on-splotch instead of true frit tints. Many will react with each other to produce the same sludgy brown, grey or black.

Too many involve opal on opal, which cuts translucency to zero in pate de verre and makes the piece look painted. Or the resulting colors are just frankly ugly or really, really blah.*

20090831-ncc2In fact, maybe less than a tenth are what I’d call “practical tints,” i.e., combinations worth pursuing for my pate de verre.

A tenth of “a whole bunch” is still a lot. And that’s only for single-color tints.

Now add in tints that involve three or more colors of frit, which is mostly what I use, and the possibility count becomes “a whole bunch plus a whole bunch more plus a whole bunch more than THAT.” Worse, whenever I have a solid color field I tend to “drift” the color, i.e., combine lashings of pure color with frit tints in layers, to add depth and interest.

So if I do nothing but make color tests constantly, keep four kilns going without stopping, until I’m 98…I probably STILL won’t get to the blues.

Well, at least now I don’t feel like such a slacker.

20090831-ect1samplemonumentI have modified my sample shape, at least. A year or so ago I abandoned the classic wedges and ice cubes that most casters use for samples and instead have opted to make flat tiles with texture like the ones shown here.

I find they’re better for visualizing how the color will look in a real piece, and the changes in thickness give you an idea of what some depth will do to the shading. They also let you play with surface finishes–firepolish gloss on the smooth back, coldworked, velvety smooth fronts.

The results are infinitely more satisfying on many, many levels. I like looking at them, handling them, arranging and rearranging them, checking the way the light passes (or doesn’t pass) through them. I’ve also noticed other people enjoy playing with them, too–one neighbor plunged up to her elbows in color samples last week, saying “They just feel so good.” (One tried stringing the Warm Peach sample on a chain as a pendant. It was way too big and heavy but I got the impulse.)

So…I’m working on ways to exploit that. In the meantime, I need to get these things up on the wall because honestly, I think they look good just massed like that. I’m gonna get them mounted, maybe even make up sets for sale. We’ll see.


*I was politely chastised for accusing Dense White of producing tints that were “nasty” and “dead-looking.” It does that for me, despite the rest of the world’s ability to use it to make ethereally dreamy pieces I love.

Of course, in my youth I was also clobbered for telling a doting mother that I wanted to photograph her toddler because he was so ugly he was adorable. I have since developed slightly more tact, but apparently only for people’s children, homes and small animals. When it comes to peoples’ glass, I’m apparently as brutally honest as ever.



  1. kim November 7, 2010 at 5:18 pm - Reply


  2. Cynthia November 6, 2010 at 10:01 am - Reply

    No problem–Antique Amber is relatively simple, but it’s what I call a “drift” mix because it’s both blended frits and drifts of other colors. That means you’ve got to be very careful to test and weigh proportions and even then it’s going to look different, particularly in larger pieces. (in other words, your mileage WILL vary 😉

    For each tile, you weigh out 90% BE Medium Amber fine frit, then in powder, 5% Carnelian, 2% Woodland Brown, 2% Pimento Red and 1% Light Coral Orange (or Crystal Clear, depending on which you have on hand).

    Start by weighing out 70% of the Medium Amber by weight and setting it aside. Put the rest of the MA in a lidded jar, schpritz in some water, and sift the Pimento Red over it. Shake it really, really well and check frequently to make sure the Pimento powder is evenly distributed over the MA.

    Now start filling the tile. Sift or fling a little bit of the Carnelian and Woodland across the face of the tile, fling a thicker amount of the MA mix across that (vary the direction of your flings), layer pure MA frit on that, then keep interlayering them like that until you’ve filled the tile.

    It takes some practice and a lot of testing to get a look you like, and you need to make all the tiles in the same period of time, if possible–your filling technique will vary if you have long intervals between making these tiles. if you do, you need to make sure you mix batches together before applying them to the wall, or people will be able to say “ahhhh…these are the tiles she did before Thanksgiving, and THERE are the Christmas tiles…” 😉

  3. kim November 5, 2010 at 8:12 pm - Reply

    Would you perchance be willing to share your recipe for antique amber?? It would look really nice for some tiles I’m making for my bath.

  4. Cynthia September 29, 2010 at 1:06 pm - Reply

    Hey, Sunny. Yeah, I get a lot of requests to do a book and if I can figure out how to do one that’s specific enough for a broadish audience, I will. The books I’ve already done are in the high tech space, mostly, but I’ve always wanted to do one with glasswork stuff. Thanks for the suggestion.

  5. sunny strapp September 29, 2010 at 2:08 am - Reply

    Hi ya C, foto documenting everything is the great basis for a techie book, to help all us strugglers. Why ignore a knowledge goldmine? If you are organized already, find a slave to put it in a “growing” book project. Have you no slaves?


  6. Cynthia September 28, 2010 at 1:09 pm - Reply

    French Vanilla? Ahhhhhhhhhhhh. I love French Vanilla to death, it’s a color I use a LOT…but it’s reactive as hell. That, and not the binder, might be causing your reaction.

    Depending on what frit you mix it with you’ll get everything from dark chocolate to…(drum roll)…grey. It’s a sulphur glass, which means that if you mix the frit with copper or lead glasses (or silver) you’ll get a sulphide reaction where they touch. IOW, if the blue looks aqua it’s probably got copper in it, if it’s cold white, pink or purple or a warm, earthy brown there’s a good chance it has lead in it…and the glass will go dark on you.

    How dark depends on how well it’s mixed, and how much of the metal is in the glass. Bullseye makes a good reactives chart for its glasses that explains it better than I can:

    Anyway, I’ll bet that has something to do with your problem. If you’re working in layers, you can avoid it by simply putting a thin layer of clear powder between the offending colors to separate them. Unless they’re really strong (the new reactive glasses, for example), that will stop the reaction.

    The trick with really getting great skin tones, I’ve found, is to mimic the way real skin is built, with layers. I’ll build up from the back with clear frit, then sift on a thin layer of orange-red (Pimento, Tomato, Red-Orange, whatever). Then I add a dark purple (violet striker, deep plum, etc.) wherever I want shadows or hollows (eye sockets, under the cheekbones, inside the nostrils). After that, I can mix and layer my skin tones. I favor Light Peach Cream and clear–LPC is slightly reactive so I add a bit of turquoise or light aquamarine to it to tone down the peachiness.

  7. Elizabeth Kshatriya-Ward September 28, 2010 at 11:38 am - Reply

    Thank you for your reply. Sorry I didn’t get back sooner, but I’ve been a little busy. I had an Art Fair and taught a wire-wrapping class, among other distractions.

    As to mixing frits, after seeing your website, I solved a problem I had almost immediately. I have been looking for a convincing skin color, and mixed up Transparent Amber, one batch with opal white and one with clear. Both were successful, the white mixture had a more “Caucasion” look, and the clear mixture a bit more “tanned”. I will experiment more when I can.

    I have tried to find food grade CMC here in Albuquerque, no luck. I tried gum arabic, and found no difference. I actually use Bullseye French Vanilla as my test frit, and do a freeze and fuse, or use Fusetac as a binder. That works very well, but it isn’t as hard as CMC or gum arabic, so I can’t rework or refine the piece before firing.

    Although I do soak at 800 degrees with my peep hole open (I have a small Aim kiln), I am thinking it just might be still not oxidizing enough to burn out completely. The pottery supply owner where I got my CMC thinks that might be the case. I’m concentrating on production at the moment, but next opportunity I’ll try opening the lid a little. I will try a smaller amount of gum solution also.

    I actually don’t use a classic Pate De Verre technique, but a variant of Freeze and Fuse. I use two part silicon molds, freeze, and then unmold. The binder then allows me to let the pieces dry, do some judicious alteration if needed, and then fire up when I get a kiln load.

    I use the pieces to assemble jewelry with simple fused glass backing, or as elements for adding to larger fused glass objects.

    I don’t get much time for the computer right now, as I am trying to work on a successful and saleable product. My husband and I are retired, and both of us dependant on Social Security checks, so if I’m to continue working with glass, I have to make it at least pay for itself!

    Thanks again,
    Elizabeth (Lisa, to my friends!)

  8. Cynthia September 13, 2010 at 11:19 pm - Reply

    Hi, Elizabeth. Barry’s really helpful and pretty good with this, so if he doesn’t get it, I’ll probably not get it right away, either.

    Dunno who told you that Bullseye frits don’t mix well, but they mix wonderfully, to the point that they become just as much a color palette as watercolor paints (especially if you fill in the color gaps with Uro90 frits). There are some tricks to mixing, though:
    –You have to pay careful attention to reactive colors. Mix the wrong glasses together and you will indeed get grey or dark brown or speckles or something in between.
    –I primarily mix transparent colors, which makes sense if you think about it. You can’t really “mix” powdered glass, you’re simply distributing the different colors so that you see one through the other, making a new color. You can’t see one opaque through another, so what you wind up with is polka dots instead of a real mix.
    –Opal glasses CAN be used to tint frit mixes quite successfully, but I find I have to keep the percentage of opal relatively low. There has to be enough there to intersperse evenly among the other colors, but if you get past about the 10% mark you start getting splotches again. The best opal/transparent mixes seem to come when the opals are about the same saturation/value levels as the transparents.

    Your problem could be the binder, I suppose. One way to test is to use the identical frits in a freeze-and-fuse with water and a pack with binder, then fire both in the same kilnload. Use the same mold, same everything else. If they don’t look the same, you’re right, it’s probably the binder.

    I use gum arabic–I buy the less expensive printer’s GA, which isn’t as pure, then I dilute it with water. It only takes a few drops of GA to perhaps a quarter-cup of water to make a good binder.

    If you want to eliminate all possibility of contaminants and still use a binder, go to a pastry/cake decorating/restaurant supply store (whatever’s handiest) and get some CMC (carboxymethylcellulose). Food-grade is the purest. Mix a batch of that like you would old-fashioned gelatin (which also works, BTW) to make a gel, and try that. CMC mixes vary, so you’ll have to experiment to get the right consistency.

    Try your piece with the CMC and see if that helps.

    But I really wonder if it’s not something else. Just out of curiosity, what colors are you using?

    Also…if you’re using a pate de verre mold, the glass doesn’t HAVE to be placed in the mold with a binder. I tend to reserve binders for when the glass has to stick to the sides, or I’m being really finicky with placement in second or third layers. Otherwise, I prefer using it dry–I have more control and I don’t have to worry about contaminating the glass. You might see if it works better for you dry.

  9. Elizabeth Kshatriya-Ward September 13, 2010 at 10:59 pm - Reply

    Hello, Cynthia!
    I am a glass artist, working with fused glass since the late 80’s. I found you on a thread on Warm Glass. I am currently working with small Pate De Verre inclusions for jewelry. I started with “Freeze and Fuse”, and then discovered Barry Kaiser’s glass clay formula in “Glass Patterns” magazine. I tried his formula, which seems to work easily for many, but found that my pieces came out grey. I tried other binders (gum arabic, also commonly used), and still got grey. Glastac works well, but the pieces are quite delicate. I tried soaking at 800 degrees, hoping to burn out any carbon. The pieces looked like the grey had burned out, but at 1300, they were an even deeper grey.

    I emailed Barry, who was very gracious and tried to help, but he couldn’t figure it out.

    Currently, I am using Glastac which works for me relatively well, but I continue to search for an answer. The sturdiness of the clay formula allows for some refining before fusing, which the Glastac formula does not allow.

    What interested me is your work with color mixing. I am only recently getting into it, as I was told Bullseye frits do not mix well. I am learning, yes and no. Some colors react badly with each other, and some work fine.
    Your color work has encouraged me to continue working with it. Thanks!

  10. cynthia March 29, 2010 at 10:45 am - Reply

    Thanks, Mary Lou…it’s a little easier to do it as a caster, I think. I have ready-made forms for test tile molds, and they stay set up in my mold-making area. Any leftover investment immediately gets slopped into the tile mold, so that after three or four molds I’ve got another blank for tests. I pretty much turn one out every week or so, possibly more often.

    There are times, though, when I think I’m doing more testing than actual making, and that gets frustrating.It’s only been in the last six months or so that I’ve started to be able to predict what the glass will do without making a bunch of tests (and be reasonably accurate) in the warm ranges. I’m still working on the cool blues. 😉

  11. Mary Lou Burnside March 29, 2010 at 8:15 am - Reply

    Cynthia, I love your work and I admire tremendously your ability to research and develop materials and product, for your work. I don’t personally know many successful glass artist but I do think the key element in being successful in terms of controlling and creating the results you expect, is the willingness to spend vast amounts of time experimenting. I have seen the results of this at Bob Leatherbarrow’s studio. He has numerous test tiles that he has made over the years, identified and mounted and when I took a course there they were a great help in selecting colours. I have started to develop my own tiles but I do get sidetracked when the desire to produce something overcomes me and I just charge ahead to create something for instant gratification. Patience is indeed a virtue. Sorry for the rambling and I do know there are other artist out there with similar work ethics like yours and it’s probably their work I admire the most. Mary Lou

  12. Linda Steider September 23, 2009 at 7:14 am - Reply

    Looks like a beautiful box of candy, Cynthia!

  13. Kathleen Krucoff September 7, 2009 at 7:53 pm - Reply

    Wow! Even if you could get to all of the samples, where would you put them?

    I do love this and how you keep track of it all. Invaluable.

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