You really don't have to clean your brushed at all, just wipe them on a towel or rag. If you really want to clean them you can:
Wash them in warm sudsy water or use a "saddle soap" on them (found at Michaels); Use thinner on them and wipe them dry: Just wipe them but if you do you will only use that particular one for the same color/tone paints.
A lot of us have certain brushes for certain colors (ie: blush, veins, fleshtones--dark or light, etc).
Red and blue paints are highly pigmented and so will/may seep in faster and be harder to remove.
Matha, I know one reborner who says she never cleans her brushes. Unfortunately, I live in the desert so there's a lot of dust that just seems to penetrate everything. I use dishwashing detergent like Dawn, Palmolive, Joy, etc. and apply it directly to the bristles. I gently massage and then rinse until the color is mostly out. I say "mostly" because of what Buffington said about the paints being highly pigmented. There will be some residual color that seeps into the bristles, but that should not alter the paint color when you use the brush again.
The odorless paint thinner also works. I personally like the Mona Lisa brand.
Hope this helps,
Linda
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Linda Dreyer~ Forum Moderator Secrist Certified Newborning Teacher & Dealer Apple Valley DW Dealer Play Days Dolls & Collectibles PlayDaysDolls.com (Current Avatar: Erinfrom Secrist Dolls)