Pigment fixative-- what do you use?

A pigment fixative's job is to help pigments flow into micro crevices on a surface. A fixative doesn't have a chemical that sticks pigments to a surface. You can use any liquid with a low surface tension as a fixative as long as it doesn't damage a surface. I personally use odorless paint thinner as a fixative because it doesn't damage acrylic paints. I sometimes use water.

I've never had luck with thinner as a fixative--better than nothing but the stuff still smudges. A true fixative is basically a clear coat of paint that forms a thin film, giving the pigments some protection in addition to adhesion.

Believe it or not I've successfully used hairspray as a fixative (but I don't necessarily recommend it). Artists have long used hairspray to fix their charcoal drawings or pastel works. It's certainly cheaper than the professional artist's fixative, but hairspray isn't formulated for long term use.

My personal favorites are AK Interactive's pigment fixer and Humbrol's Matte Coat thinned 50/50 with Humbrol thinners. I couldn't tell you which is cheaper, but they both give rock hard protection.

Some pigments are so fine you don't need a fixative.  Rouge is one.  After you remove excess, try picking the model up in the area of the weathering pigments. If it doesn't come off on your fingers, you probably don't need a fixative.

You can usually tell as you apply it how fine the pigment is ground.

BTW, if the pigments are really fine, be careful with application.  The real fine stuff is hard to get off of areas you don't want it over :-(