Measure and mix

Start with the amount. A rectangular mold holds length times width times depth, and one cubic inch is 16.4 ml. The resin calculator does this for round, square and odd shapes and adds a margin for what stays in the cup. For a mold with no simple shape, fill it with water, pour the water into a measuring cup and read the volume. Dry the mold completely afterward.

Then the ratio. Labels give it by volume or by weight, and the two are not the same number, because Part A is denser than Part B. One popular art resin is 1:1 by volume but 100:84 by weight. Measure the way your label says. The mixing ratio calculator splits any total into Part A and Part B. A wrong ratio is the usual reason epoxy stays sticky.

Stir slowly for 3 to 5 minutes, scraping the sides and the bottom of the cup, until no streaks are left. Several makers ask you to pour the mix into a second clean cup and stir again. Fast stirring whips in air. At the end, do not scrape the walls of the cup into the mold: that film is the least mixed resin in the cup and it leaves soft spots.

Ready to move on when: The mix is clear with no streaks or swirls, and it was measured exactly the way the label says.