dawnt
Posts: 5863
Joined: 7/30/2005
From: Iowa
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Grisaille is a painting technique using layers of black, umber or while enamel and silver stainers on clear glass. It isn't something I've really done for my own pieces, though I think it is really a lovely technique and very effective in borders etc. It is incredibly tedious and time consuming, which is probably why I don't do it unless I have to.  In this case, I had to, for the repair of a vandalized church window made around 1868.
It is a 3 step process. First, you do the "tracing" layer, usually in umber or black. (In this case, most of the tracing was done in a pale gray/white, which reads dark when backlit.) Generally, since grisaille features a lot of repeat patterns, you have to cut frisket and airbrush or paint....or if you're dong a ton of them, make a silkscreen. Then once the enamels have dried to a loose powder, peel all the frisket to expose the design. The enamels come in powder form and you have to mix in your own binder, (gum arabic), and medium. For this kind of thing, I like to use vinegar, because it makes it stick to the glass nice and hard. Once the tracing is done, you fire that up to 1250-1400 degrees, depending on how much gloss you want.
Step 2 is applying a very thin "mat", usually in white. You mix the pigments the same as in step 1. You can do this either with a badger blending brush or an airbrush. (Airbrush is a lot easier, but the enamels are nasty toxic things, so you have to decide which is the lesser evil. I have a good powerful spary box, so airbrushing it is! ) Once it is applied...so thinly that it looks like frosted glass....you let it dry, then scrub off areas that will highlight the entire design. This is pretty loose and organic and almost messy. A big contrast to the previous step. Then fire them up again.
Step 3 is applying silver stain. It is a chemical compound containing real silver that actually changes the composition of the glass to color it. Back in the day...the ONLY colors of glass were variations of amber, from pale pale yellow to almost deep red, produced from silver stain. You kind of wash the stain on the reverse side of your previous painting then fire IT up, upside down. Silver stain contaminates everything, so you have to have a dedicated kiln shelf for it, and have to be very careful in fiber kilns so that it doesn't leave residue that will mess up subsequent glass firings.
And voila....there you have it....just like the old Medieval monks did it!
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Grisaille repair work - 
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