Thanks to Brian Pate, and to Don Mitchell who suggested I call him, I’ve started vacuuming my castings when I pour them. Brian indicated that he liked to vacuum before and after pouring, but I’ve found the pre-pour treatment makes little difference. The post-pour treatment, on the other hand, dislodges all sorts of bubbles from the deep recesses of my molds.
The resin is Smooth-Cast 310, which has a long pot life of 20 minutes. It also has a commensurately long cure time, which, it turns out, bothers me more than I want to admit. However, the process takes about five minutes so this wouldn’t work with a faster resin like Smooth-Cast 300.
My vacuum isn’t strong enough to collapse every bubble. So the best approach seems to be to pull the vacuum, watch the bubbles foam to the surface, and then release the vacuum and push any remaining bubbles away from the backs of the castings. You can see that there are still a couple of bubbles in the collection pictured here, but the later attempts have had zero.
Until that bad pour.
For some reason, the previously trustworthy jars of resin started dribbling down their sides and into the mixing cup. This lead to a profoundly unbalanced mix of A and B, which didn’t set right, and ultimately damaged the surface of the molds. So, lesson learned: it is better to abandon a potentially bad batch of resin, than pour it into the molds anyway.
At any rate, there is continued forward progress, and I’m sure I will get there. Eventually.