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Velour is a funny/odd substrate in that pastel will all fall off when you don't want it to and will cling tenaciously when you want to remove it! I swear it seems to know the difference! So, to prevent problems, I normally spray with fixative between layers then leave the top layer alone or spray very lightly.
I reviewed the SpectraFix fixative not too long ago here on my blog and that is what I used on this portrait. It's about the only fixative I've ever used that doesn't change the color of the pastel and I think it's the best fixative out there.
However, even with the utmost care, it can "sputter" and leave large drops of the fixative on the painting. I've had it happen both on paper and with the velour and it's very difficult to correct as the spots show up clearly. There's not much you can do to correct the spots on paper and even going over the spot with more pastel sometimes doesn't cover it completely. Normally it's a bit easier on the velour, fortunately. I waited for the spots to dry completely then took a stiff bristle brush to gently brush the fixative off as much as possible and to sort of fluff up the nap. I can add back pastel if needed to cover completely but usually the velour doesn't need it.
This time it didn't work that well and the spots were really visible on the background where there was no pastel to begin with. I ended up adding a halo effect with pastel around the dog to hide the spots. This worked, fortunately.
I'll know in the future to shield any areas without pastel to protect from these spots!