Cold cast troubles-Polishing issues

tubachris85x

Master Member
RPF PREMIUM MEMBER
I still consider myself a newbie when it comes to cold-casting, but I've had a decent handle of it for at least a few years now. I've only recently created my own custom sized mandalorian armor plates, made molds and produced cold cast pieces from for my costume.

Due to the time constraints of needing to finish the suit for Celebration, we were only able to knock out one set of casts, but I found an issue- Despite having mixed properly, I was NOT able to get anything more of a dull-sheen on the plates. Having followed the same exact mixing ratios I've always had excellent results, but this was before I ever had to use fiberglass in conjunction w/ the CC process. Nevertheless, I was a bit disappointed with the results, especially when I was working on another vendor's CC jango armor for the girlfriend, which shined up remarkably well.

I believed this was caused by one thing-my casting process. I had made a thread about this awhile ago, about using Urethane resins and backing it with epoxy/fiberglass. It actually works amazingly well after doing subsequent tests. My belief is that, on my very first pulls, I was treating the urethane layers the same as one would be for doing a traditional roto/slush cast; waiting for the layers to become tacky, not fully cured, before moving onto the next application. We did about 3 layers of urethan- 2 CC, 1 black tinted and then let that cure before adding the epoxy. I will note that the epoxy (epoxamite 101) get's stupid hot. Looking back on this, the fact that we didn't allow the layers to fully cure with the addition of epoxy that heats up like the sun, had an adverse affect on the CC layers- resulting in a poor ability to shine it.

So, I did another test, letting each CC layer cure (I was using both pectoral armor molds). One I did NOT dust w/ powder and the other I did dust w/ powder. I let the CC/urethane layers sit overnight and then added the epoxy/fiberglass. What I found after demolding is that I was now able to polish one of the pecs to a near mirror shine like I wanted, but the other one, the one I dusted the mold for, retained it's dull-sheen despite spending a good amount of time to polish it. I found that using the aluminum polish (Mother's) on that particular piece dulled it even more. I had just used that polish compound to get a mirror-like shine on the other piece.

So this aspect is confusing me. I've dusted other molds before and got the nice shine I like without issues, but it's a reoccurring problem, mainly with that one particular mold.

I just did cold-cast brass castings yesterday, and they came out great for the most part. I did not dust the molds for either pectoral piece and one I can say still comes out better than the other in terms of shine

Has anyone had this issue before? It's a conundrum for me, and can't seem to determine the cause...
 
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Collektor

Active Member
Have you tried lightly wiping down the resin casting with mineral spirits and then buffing with 0000 steel wool? That usually brings out the metallic sheen on cold cast parts.
 

tubachris85x

Master Member
RPF PREMIUM MEMBER
Have you tried lightly wiping down the resin casting with mineral spirits and then buffing with 0000 steel wool? That usually brings out the metallic sheen on cold cast parts.
Never used mineral spirits before, but I always use 0000 steel wool as the starting point
 

Collektor

Active Member
According to Smooth-On, the mineral spirits slightly soften the surface of the resin and it makes the polishing easier. I haven't used it myself, as the one cold cast I did polished up just fine with the steel wool, and I was going for an antique bronze sort of finish anyway.
 

tubachris85x

Master Member
RPF PREMIUM MEMBER
According to Smooth-On, the mineral spirits slightly soften the surface of the resin and it makes the polishing easier. I haven't used it myself, as the one cold cast I did polished up just fine with the steel wool, and I was going for an antique bronze sort of finish anyway.
Hmm...it's possible. Unfortunately I don't have mineral spirits. I've never had issues in the past using the same resin. Maybe it could help, but I'd need to get some to test it.

I just did my first cold cast brass pieces which came out fairly decent
 
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