Tinting the gold leaf size

[Robert Schwieger]

Just curious: method of tinting gold leaf water size. Light fastness, etc.

[Dan Seese]

Robert, I'm not sure I've ever heard of tinting gold leaf water size, nor am I convinced it could be done - at least evenly. The majority of the water size is going to run down the glass. What remains of the flooded size will hold the gold to the glass but I tend to think that pigments added would somewhat compromise the quality of the gild. It might be worthy of some experimentation with a universal pigment which is water soluble - but of course your carrier will simply be the water itself.
Something you could try (which I believe I've done years ago with some success) is treat the area you want to water gild with a clear window varnish tinted with the color you want to use. I had used transparent screen printing ink for tinting, and the lightfastness will depend on what you use. Allow that area to dry well - maybe a couple of days - before you attempt a water gild. It won't be as bright as a normal water gild but at the same time won't be as "dead" as an oil size. (Kind of like when you apply damar varnish, do some tooling of the varnish and let it dry before following up with a water gild.)
Just a thought about what you might try.
Experiment.