Re: Epoxy Brand
I've been using Devcon brand for many years, as I can get it locally at hardware stores. However, I don't use the 5 minute stuff. It yellows badly, and I often coat painted poppers & such with epoxy, so I don't want it to turn yellow. Plus, I prefer to do epoxy work in large batches, coating as many as 50 flies at a time, and 5 minute epoxy is not good for doing this. Instead, I use the 60 or 90 minute, which takes longer to set up, but when mixed properly, stays clear for a very long time. Seems the faster the set time, the more & faster it yellows.
I have a popper body that I made several years ago, painted white & epoxy coated & it still looks white. Although it probably has some yellowing, but not enough to notice a significant change.
I've not had the issue you've had, except when thinning with alcohol that has a higher water content, such as isopropyl rubbing alcohol, and the milky white only seems to stay that way until after it sets, then it gets clear as it hardens. I generally only thin epoxy when using it to coat popper bodies.
I now opt for thinning with ethyl alcohol sold as camp stove fuel, which has a very low water content.