Jumping in here on one of my favorite subjects:
I never attempt to “fix” my pigments as that (just like in pastel illustration) tends to make the pigments loose much of their “punch” or disappear entirely.
SIDEBAR: I could do an entire thread entitled "How do you pick up your models?"
I do mostly armor and model railroading so usually my paints are all flats with a final coat of matte clear sprayed on VERY DRY. *(Meaning hold the spray far from the model ~18+ inches~ so the paint falls on the model in a very dry manor giving a matte surface with a nice almost microscopic rough “tooth” surface.
The pigments can be burnished (scrubbed) into this toothed surface for an ALMOST permanent effect! (Yes, if you try very hard you can rub the pigments off.) Here again I would ask how you handle your models? Do you pick up your models; like grabbing a Coke bottle OR do you go in under the front and rear ends with your fingers like a double forklift pickup?
Besides, usually if the pigments are disturbed they can be easily repaired in just a few seconds. (I always take my pastels with me to any model competition in case I have to make a repair and then also repair the weathering after that. ~ Or in case a judge puts his/her grimy fingers all over my model.)
The famous Model Railroader John Allen used to say “Dust is weathering! DO NOT TOUCH my models!” He had certain ways to pick up his models so as not to disturb the “weathering”, I use the same approach with my models.
Some recent work:
Using “dust” pigments to highlight detail in black objects as shown above.
(It’s also great for intensifying rust effects.)
Shifting/fading paint colors using pigments.
Grumbacher “Soft Oil Pastel Set” (still available on eBay) I purchased this set around 1974 and with the exception of replacing a few sticks down through the years this set has handled all my model weathering needs ever since.
NOTE: Purchase ONLY “Soft Artist’s Oil Pastels”. Everything else is just glorified sidewalk chalk.