we know that powdered masonary pigments can be mixed with plaster.............will Tempura powders do as well?
Short answer - you almost certainly can, but you may need to adjust the water or additives in your plaster.
Tempura the Japanese dish and tempera the paint are only thinly related (by using egg as the binder in both cases, and by historical etymology).
Interestingly, the actual pigment powder in dry tempera powder is the 'same thing' used for frescoes... which are, of course, paintings with the colors fixed in the surface of fresh plaster as it cures chemically.
The difference is that the tempera powder has been pre-ground together with the binder (in classic tempera paint this was egg yolk or white) so that 'just adding water' gives you paint that will stick.
Most 'commercially available' tempera powder won't be using yolk as a binder, though -- it will likely be something like a dry white glue. And many such materials are quite suitable for use as strength-increasing (e.g. 'acrylic') additives in concrete, mortar, and yes, plaster.
What you need to do is identify what the specific binder in your chosen brand of 'polvore' is ... it may tell it on the package, or the maker's Web site, or via a request to their customer service. However I think it so likely that the binder will be 'compatible' with whatever plaster formulation you want to use that a simple text mix of a couple of ounces would tell you all you'd need to know.
For the record, I've used various colored materials to pre-color scenery plaster since I was 'turned on' to the idea (I wish I could give credit to the person who wrote the article mentioning the idea -- probably in the '60s or even earlier -- but I don't remember, so consider this 'passing it forward' on the shoulders of giants) I believe the original idea used Rit dye rather than art pigment, and I don't see why you couldn't combine powder and dye together.
(Something else to test is whether the approach to making 'stone' with sifted-together pigments ground to appropriate 'scale' size plus metallic powder in a translucent binder will work with tempera pigment -- I suspect it is ground too finely, to make 'mixable' colors, so all you'd get is the usual drab that comes from mixing too many absorptive colors.)
Black tempera paint powder is part of the finishing process to Brandon Foam rocks. These use a casting foam in molds rather than plaster. The tempera powder is brushed on after the foam casting is set and then mostly washed off, leaving a small residue in the cracks and depressions which look like shadows and accentuate the depth of the casting.
It takes an iron man to play with a toy iron horse.
Yes, use it for zip texturing myself.
You could use craft paint from Wally World.
Henry
COB Potomac & Northern
Shenandoah Valley