I've created a mold to cast some organ drawbar tips using HS-3, and have cast several using Alumilite White and RC3-Black. They're pretty decent - the front and back look almost perfect, but the sides have what look like tiny pockmarks. I can see that these are actually in the mold, not a result of a problem with the casting. Am I correct in assuming that these are caused by air bubbles. It's odd that only the sides, which are vertical, have these - the curved surfaces are completely smooth.
Any suggestions for correcting this? I'd really rather not go to the expense and hassle of using a vacuum rig. You can see a photo with the link below. I've shown three - the one in the middle is the original, the two on either side are the castings.
If you still have some HS-3 and the sides are smooth/straight, you can mix up a very small amount (or make a small mold of something else) to fill in the holes. There's a couple things you can do.
For fixing the mold itself: You'll need to open up the mold and carefully dip in some of the HS-3 to fill the bubbles on one side and let that cure. Or to speed up the cure of a small surface fix, put it in the microwave (if it isn't too big and will fit) and zap it for 30 seconds on high. A damp paper towel (not wet to where it's dripping but still has a lot of water in it) would be good to put in there with it as it helps. Let it air for a few seconds or so while you check the paper towel is still wet (rewet if needed) and then zap it again for 30 seconds on high. Be sure the mold is sitting up on the side so that the inside side is level. Once one side is done, do the other side and it should fix the mold itself.
For fixing the castings: Mix up a very small bit of the Alumilite White and RC3-Black - use whichever one matches the not perfect castings. Then just smooth a bit over top of the problem areas to cover it. Smooth it with either a craft stick or your gloved finger to get it right. Let them cure normally and they should be good to go after 30 minutes or so. Be sure to wait longer for this as it will not have the extra heat the resin usually creates to cure faster like it normally does so it just takes a little longer to cure.
I hope that helps and let us know if you need any more help and how they turn out.