Making Flat Acrylic Glossy?

The gloss of a paint is controlled by two things:

1. type of binder
2. type of pigments

What you are doing is adding a binder that produces a glossy surface. This also reduces pigment load (the paint will become more transparent and have less hide). As long as you don't run into compatibility problems, that's essentially the only drawback. In the case of some paints, a small addition of Future may also improve coating adhesion and durability.

Silicone oil is sometimes used as a gloss enhancing additive. I strongly recommend against trying this, because the amounts added are very small, compatiblility is more likely to be an issue, and the surface will be very difficult to overcoat with anything. 

Triarius wrote:

The gloss of a paint is controlled by two things: type of binder type of pigments What you are doing is adding a binder that produces a glossy surface. This also reduces pigment load (the paint will become more transparent and have less hide). As long as you don't run into compatibility problems, that's essentially the only drawback. In the case of some paints, a small addition of Future may also improve coating adhesion and durability.

That makes sense, and I suppose that's why a flat (undiluted, or very slightly dilluted) 1st coat worked best. 

 The Future also seems to thin the paint slightly.

 I hadn't considered the adhesion and duirability aspects. That's a bonus. I always use a primer to improve these weak areas of Acrylic.

One other benefit I may have found is when I put the paint on too heavy (not that good with my double action yet), the Future seemed to level it out when it dried.

Silicone oil is sometimes used as a gloss enhancing additive. I strongly recommend against trying this, because the amounts added are very small, compatiblility is more likely to be an issue, and the surface will be very difficult to overcoat with anything.

I've learned from experience, never put anything with silicone near paint or anything I wish to paint. I don't even like the two words in the same sentance.

The acrylic polymer in Future has a very low viscosity. It's initial cure is slow, then it accelerates to the point of tack-free, then slows down again to full cure in 24 to 48 hours. That explains your apparent thinning. I hope the chemist(s) who developed Future were hugely rewarded—they deserve it.

I've even heard of some people who add their own pigments to Future, essentially making their own paint. Even I'm not that crazy! 

The amount of silicone we put in a test batch (about 1 quart to half a gallon) was usually on the order of one to two drops. That's not much per 1/4 oz. 

Triarius wrote:

I hope the chemist(s) who developed Future were hugely rewarded—they deserve it.

I agree. Cool stuff! They probably didn't even realize its versatility at the time.

 Thanks for the info Ross.