thank you very much George! I don't have gum tragacanth though, I would only get it if it made stronger chalks than gum arabic, but would it? My complaint about my pastels is that they release too much colour too fast, I guess tragacanth would make that problem even worse?
What a great idea about the nozzle!!!

Could you say more about your Roman black pigment?
Is there a way to get it in pieces rather than powder? Who could I ask?

Also is this roman black brownish in colour? I remember at Zecchi they offered me a black chalk that was a sepia colour, but that doens't work well with a trois crayons technique which requires a cooler or neutral grey-black.