I was asked for recommendations on casting resins by a member in a PM and thought I'd answer here as the information might be of interest to others.
I am currently using Silpak's Silcast II for casting shells, kit parts, prop parts, for pretty much everything. It's a great general purpose casting resin. Naturally white in color, I add some black tint to the bottle to make the parts grey. It's a little easier to see surface flaws in a grey part. It has a 3 minute pot life before it starts to set but you still need to work pretty fast to mix and pour. Silpak has a variety of other resins and I've tried most of them, settling on Silcast II as my favorite. It doesn't hurt that SilPak has an outlet not far from my Day Job and I can get there, pick up resin, grab a burger and get back during a lunch break!
www.silpak.com
Alumi-Lite Regular (Tan) is another resin I like. Back in the "old days" it was my go-to resin for most things. It's thinner so it is a little easier to work out bubbles with a toothpick if you're not pressure casting. It does kick off faster so you've got to mix and pour really quickly, especially if you are mixing larger quantities or working in hot weather. I've found that even though it kicks off faster it can take longer than Silpak to fully cure in thin parts. The thinner the part the less heat generated by the cure and the slower the resin take to fully harden. Alumilite is stocked at many hobby and craft stores and you can order it through Amazon, in addition to their website.
www.alumilite.com
Smooth-On is another popular line of casting resins. I've used some of their specialty resins but not their general purpose ones, though I've heard good things about them. The Smooth-Cast 300 looks like it has similar properties to the SilCast II and would work well for kit part and model part casting. Smooth-On products are sold through Reynolds Advanced Materials and they have 8 locations through out the U.S. and Canada, as well as being available online.
www.reynoldsam.com
There are certainly other resins out there that will work well, I've just found ones I like and am use to, so there's not much need to go looking for others. There are probably very few resins to be avoided, al though some may have an objectionable oder.
It's a good idea to only buy the amount of resin you think you will use up in a couple of months. Urethane resin is 'hygroscopic' and absorbs moisture from the air once opened. After a while, this moisture will get to the point that is causes the resin to foam up ever so slightly ruining castings. If you live in a humid climate this will happen faster. Pressure casting can help to minimize this foaming if you are using a tank to cast. I like to pour resin from the larger container into smaller 16 ounce plastic bottles with a capable pour spout, helps the resin to last longer and makes the resin easier to pour and measure. Most of these resins are available in small and large kits. I typically by the large two gallon kits but even with all the casting i'm doing for the Y project it can take awhile to go through a set.
I've been asked about the "archive" nature of these resins. Unlike UV cured resins used for 3D printing, cast urethane parts should last pretty much indefinitely. Just look at the models from ANH, they still look pretty good, even after forty years. Extreme heat can cause parts to warp so don't leave models in the sun or in your car on a hot day.
Urethane resins can be used at pretty much any temperature you are comfortable working at, within reason. If extremely cold, they will take a long time to cure, if extremely hot, they can kick off much faster. While I don't have the cold problems here in Southern California, there are times during the hottest days of summer where my shop can be in the 90's or higher and large batches of resin can kick off before I get it poured. But I usually don't like to work under those conditions anyway...
Other notes... as I said in an earlier post, you can get good bubble-free casting without a pressure chamber, it's just take a bit more work and you might have more reject parts, particularly parts with very thin sections.
Roto Casting is not needed for most kit part and model casting. It really only becomes advantageous when you are trying to create hollow castings from closed molds. On the Y-wing project the only part's I've roto-cast were the L'Eggs engine nose cones. Those could have been done with two part molds and pressure casting instead but roto was the fastest way to crank out the quantity needed and the molds were a lot easier to make. Silpak and Smooth-On do make specialty resins for roto-casting but I've had fine results using good ol' SilCast II with a thixotropic powder added to thicken it up a bit and help it coat the sides of the rotating mold.