I have tried Mig's Pigments on two kits. I have not used pastel chalks so I have no experience with them. The pigments seem to adhere to whatever you put them ok. The first time I used them I thinned a small spoonful down with rubbing alcohol and brushed it on tank tracks. I think I overdid the amount I put on the tracks. I thought once everything dried out that some of the pigment might come off, but I was somewhat surpised that once dry the pigment seemed to adhere without coming off. I wish now, looking back on it that I had not put so much on the tracks, but that's where trial and error comes in a bit. I am happy with the color, I used 'standard rust' with some 'european dust' added in. I just think I applied too much. Now I know what to expect and will apply sparingly on the next set of tracks I wish to weather!
The other attempt with Mig's Pigments worked out very, very well!! So much so that I cannot wait to try it again! I cannot take credit for the idea, that came from Franck Edet over on WWIIModelmaker! Anyway, you can air-brush pigments, or at least I did! I filled my Badger 350 bottle about 1/2 full of rubbing alcohol and added about 3/8 teaspoon of 'european dust' to the alcohol. The bottle now looks like a jar full of brown wash! Then I sprayed it out the air-brush on this Panther D kit I'm working. Once the rubbing alcohol dries out all you're left with is a nice light coat of dust wherever you want it! Want it thicker? Then try a few more passes. Now I put this on last, nothing else is going on the model. I'm still in 'trial and error' mode, but I think I'm going to like the results. Like to old TV commercial said "Try it, you'll like it!".
Anyway that's my limited experience with Mig's Pigments. I bought mine from The Barrell Store at www.bentbutnotbroken.com
Glenn
P.S.- a little standard rust and some light rust on the rear exhausts look very cool. I painted the exhausts Tamiya red-brown first!)