I still don't know why I didn't try this sooner, but I suppose it's better late than never. The secret to pouring up perfect, bubble free urethane belts is none other than our old pal from our resin slinging days: Baby Powder.
Yup, the type of stuff you get at Target. When you powder up a mold prior to pouring in, a force called "Capilary Action" comes into play. This magical force draws the liquid into the tiny nooks and crannies. It works amazingly well. My fear was that by powdering the mold up, I would somehow taint the pigment. When you powder a resin mold, it's not an issue, as the expectation is that you will paint the thing coming out of the mold. Not the case with this project.
Anyhow, on to the victory pics:
Here's a close up of the buckle. I challenge you to find a flaw in this pull:
And just for good measure, I trimmed out the flash so you can see how the finished product would look. It's still a little sloppy, but you get the idea.
For my next trick, I powdered up the mold for the chest emblem backplate. Booya. It came out PERFECTLY. I don't know how well you can see the micro-S pattern in this photo, but take my word for it, there is not a single imperfection in the casting.
Now that I have the technique down pat, it's really just a matter of mixing up a color that is to my liking. More experimentation. But the good news is that no matter what color they come out to be, they will be flawless, bubble free castings. Here's some shots of the next one out of the mold
Overall, I am very pleased. This has been a very productive week, and I've answered a lot of questions. I am getting VERY close to having a repeatable process for producing good quality belts, which is what I'm after.
I am just about out of silicone rubber, so I'll need to order some more from Sil-Pak so that I can finish up the chest emblem mold. I really feel like I'm on the right track now.
There's really only two components to lock down from here. I may try for a harder shore strength urethane, as the 80 I'm using still seems a little soft. I also really need to nail down a REALLY opaque red tint for the chest emblem. I can make due with what I have, but it's not quite perfect.