I have project in which I want to use epoxy resin. I want to get a white non-transparent color, pretty solid though, and I was wondering if acrylic paint is a good option to mix into the resin?
I agree with Chris H's answer, and titanium dioxide powder is one of the best solutions (it's the go-to white pigment in most things; it's what is likely coloring the white acrylic paint, so you would be adding the color without the problematic acrylic binder). People do use acrylic paint to color epoxy, and it can work, but it isn't really a good solution. This answer will be more of a supplement to Chris H's answer.
Just to note: with any colorant, you generally want to mix the epoxy first, then add the colorant to avoid having it affect the cure. A slower-setting epoxy will give you some working time before the epoxy starts to gel. Thoroughly mix the resin and hardener, and give it a minute for the reaction to start. Then add the colorant and thoroughly mix it in.
There are a number of ways to color epoxy.
Dye. These are colored liquids that leave the resin transparent or translucent, but they can filter enough light that it is hard to see through. Some people use food coloring or alcohol inks, which aren't really compatible, but you can add tiny amounts of these and get it to work (not more than a few percent without affecting the epoxy). Dyes aren't a good solution in general if you need it opaque, and white is particularly hard to do with dye.
Pigments. These are very fine powder that is chemically inert in what you're coloring. Most pigments used as colorants are opaque, blocking light from passing through. You see their color from the light that reflects off the particles near the surface. Most white pigments are mineral compounds, like titanium dioxide.
Pigments used as colorants are ground finer than most powders used for other purposes. This allows a tiny amount to be thinly disbursed and still provide good, opaque color (as well as helping it to stay suspended).
Note that most common white powders you happen to have on hand aren't likely to be good for this purpose, even assuming they don't react with the epoxy or interfere with the cure, and are very fine powders. Many loose powders look whiter than they actually are, and wouldn't look pure white when used as a resin colorant (for that matter, many clear substances look white as a powder).
If good white colorants were hard to come by, there are a few readily available materials that could be used in a pinch, that wouldn't do as good a job. But titanium dioxide is used in so many things that it is readily available in small quantities at places like Amazon. If you're going to go the pigment route, this is probably your best choice.
It doesn't take much pigment to color resin. However, using a lot of it won't affect the resin (other than to act like a thickener, potentially turning the liquid resin to a paste or clay if you went wild with the amount).
A safety note: because pigments are ground so extremely fine, they may stay suspended in the air for a long time. So if you use them, it's best to handle them in an air-controlled hood. Otherwise, wear a respirator or N95 mask to avoid breathing it.
Pigment-based colorants. These are the pigments suspended in a liquid. Their consistency tends to be "thick", like glue or paint, or even close to a paste (the higher the percentage of pigment, the thicker it is). These have the advantage that you aren't working with a messy and potentially hazardous powder, but you generally can't add more than a few percent to the resin without affecting it (which fortunately is enough).
There are two kinds of liquids the pigment can be suspended in--ones that are compatible with the resin, and ones that aren't (even though you can get some of them to work). Acrylic paint is an example of the latter (the liquid is mostly water).
The "good" liquids are ones that are compatible with the resin. Some of the commercial resin colorants premix the pigment with a small amount of resin. It doesn't take much, so the additional resin is usually in the "rounding error" of the mixture. Even then, the manufacturers recommend premixing the epoxy in the normal ratio, then adding the colorant.
So if you don't want to mess with pigment powder, pigment-based resin colorant would be a good solution, and that is also readily available.
In general, water-based products and epoxy don't mix well, and normal acrylics are water-based.
Instead I'd try stirring in titanium dioxide powder (titanium white pigment). You probably wouldn't need much, and it should be good and strong.
I have seen white epoxy before, but that was a special technical type. I don't know if it's available for craft purposes, let alone with the other properties you might need.
Just to add my 2 cents to the discussion:
I've used acrylic paints in epoxy before and had no problem mixing the paint into the epoxy. However, I did have a problem that certain (sugar based) food colorings simply wouldn't mix into epoxy. Your specific case is one of the easiest to manage, but in general epoxy is not an easy material to work with and there are several aspects you need to keep in mind:
- You shouldn't mix more than 10% (by weight) of liquid substances into the epoxy or it doesn't cure properly.
- Mixing water into epoxy makes it cloudy white.
- Some paints (especially cheap ones) contain chalk and other fillers. These have a tendency to separate when mixed into epoxy and the heavy fillers sink to the bottom while the light pigments stay suspended.
- As a consequence of all points above, you should only use high quality acrylic paints in epoxy. High quality paints usually have a pasty consistency (low water content), a high pigment content (able to tint the resin with less added paint) and finer pigments (less likely to sink to the bottom).
- Be mindful of which paint you use. Most high quality paints come in opaque, semi-transparent or transparent and there should be symbols on the paint tube to show which kind of paint is inside. If you want an opaque resin, you should get an opaque paint to color it.