Ghudra said:
You can shave really fine dust off of the pastel with a hobby knife/razor and use that with Dorland's wax medium,acrylic medium, or with white spirits.
Or used dry of course.
They tend to be a bit stubborn when it comes to adding plain water but with a bit of work they can be made into a paste, as with white spirit.
Ghudra said:
On the other hand, I could see possibly using oil pastels for some "wet" effects.
Wouldn't oil paint or alkds be simpler for this, with the assurance that they'll harden properly so less chance of them getting dust sticking to them? Come to that, acrylics + gloss medium would be my first choice for this!
Shawn R. L. said:
How much, if any, do the chalk colors change when dull/clear coated?
Depends a bit, unfortunately it's something where you'd have to test to see. There have been comments posted where the effect almost vanished but other people report that it just takes it down a notch. So it might depend on which colours as well as how much was used.
The exact makeup of the pastel could be a factor too, although they would all be pretty similar in ingredients (pigment + filler + binder) the type of binder might make a difference, hard to know.
Einion