I want to paint with Reusche weather resistant paints (e.g. stencil black, strong blue) on white opalescent glass. Probably something from Kokomo or Spectrum. I've heard more than once that glass paint doesn't adhere well to opalescent glass. Anyone have first hand experience with this subject? I can test the results for acid/base resistance, but perhaps that's not the issue?
Don, it so happens that I've done some painting and firing recently on two types of Kokomo opalescent glass. Both were streaky neutral background type glasses. I painted lettering on one with Reusche Stencil Black, fired at 350DPH to 1250 with a 10 min hold. The paint looks good, but the edges of the piece of glass, and the area directly adjacent to the letters lost its gloss. I believe this is due to those areas getting the most heat work. i.e. the edges because that's just the way it works (edges get hotter quicker) and the areas around the letters because the black paint absorbed more heat. I had two of these pieces of glass in the kiln, and the edges of both lost their gloss. curiously only the lettering-area of one lost its gloss. So much for kiln eveness. This is a kiln with roof elements too, which I would have expected to not have such an issue. But I can't think of any other reason.
So I took another piece of Kokomo that was kind of similar (I didn't have any more of the exact glass) and put it in my little test kiln with the same program. And it turned black. Not at all similar to the nameplate issue. ALmost solid black. Useless.
So Don, take my advice and don't paint on Kokomo unless you test first.
My untested/seat of the pants theory is that some opal glass is "harder" then antique or cathedral glass. It cuts differently and seems a bit brittle. So my guess was that for the paint to fire/adhere you needed to fire a bit higher then normal. Otherwise the surface of the opal glass would not get soft enough for a proper fusing of the paint.
Rebecca said that Spectrum and on Youghiogheny paint OK. Their glass is typically on the "soft" side.
Also, a lot of older paints and painters, especially those that came from a China painting background used borax as a flux. Borax burnt off in the high fire ceramic work. But did not always burn off in glass work, which then absorbed some moisture which undermined the paint.
So again my theory is too much borax and too low a firing temperature in opal glass painting..
I had a repair with glass I was having trouble matching. It was a dark beige or light brown. I sent a sample to Kokomo and was told that they sometimes got that color (called it "muddy") when the temperature was a little high. He told me what the item number was that turned muddy. (I can't remember right now.) I put some Kokomo of that number in my kiln and it matched what I needed perfectly when it came out of the kiln. So some glass might "strike," too.