The rigid version of the flexible I've used in these videos will require both a vacuum chamber and a pressure pot to get perfect castings. It is really temperamental stuff and I was not impressed with how my casts came out given the price. Even though I degassed, bubbles formed over night and as a result, the only way I'd buy that stuff again is when I get a pressure pot that can take at least 80PSI over night.
There are other alternatives like epoxy which give a good result and are much easier to use.
If you have access to a chamber, awesome. If not, you can still get good results with these by making smaller pours and building up. By applying a heat gun to the pour, you can pop all the bubbles as they raise to the surface. if the pour is too deep, then they will be visible in the final cast part after curing.
The only negatives about epoxies is -
1. They do produce a lot of heat, so they can over time burn out your soft silicone molds. I use a high shore silicone and use epoxy all the time.
2. They are prone to some shrinkage, so you may need to top up the mold prior to demolding. This is just a time thing and shrinkage does not always happen.
A plus for all clears is that clear resins take colour better than those products that turn white when they cure. With clears like polyurethane or epoxy, you don't lose any colour intensity. In other words, black tinted resin comes out black once cured, not dark grey.
