Using Smooth-Cast 325 Colormatch

Squall67584 · Post by **Squall67584** » Wed Nov 25, 2009 7:00 pm

I made a couple of molds of small parts about a couple of months ago, and used the 325 colormatch resin to cast a few of them up today. I got the colormatch because that's what the art supply store had in stock. The first set of casts turned a solid white and frankly still slightly sticky six hours later. But the second through fourth batches were all semi opaque and are dry to the touch. I'm guessing I didn't get the mix right for the first batch, but it seems weird that they turned a solid color while the others didn't. Anyone ever have something similar happen?

vaderman · Post by **vaderman** » Mon Nov 30, 2009 4:37 pm

I does sound like you did not mix the first batch well. I have had it do the same thing. Also, the color match will tend to have air bubbles in it unless you have degased your molds and are pressure casting.

Scott

Joseph Osborn · Post by **Joseph Osborn** » Mon Nov 30, 2009 5:45 pm

Squall67584 wrote:I made a couple of molds of small parts about a couple of months ago, and used the 325 colormatch resin to cast a few of them up today. I got the colormatch because that's what the art supply store had in stock. The first set of casts turned a solid white and frankly still slightly sticky six hours later. But the second through fourth batches were all semi opaque and are dry to the touch. I'm guessing I didn't get the mix right for the first batch, but it seems weird that they turned a solid color while the others didn't. Anyone ever have something similar happen?

three questions:
1) Was the mold brand-new?
If Yes,
2) Was the mold tin-cure rubber?
If Yes,
3) Did you post-cure the mold at around 125F for a few hours before use?

If you answered "Yes" to all but the third question, then the tackiness in your casting is from the excess moisture in the rubber that inhibited the cure on the first casting. It usually goes away after the first cast, so that's why you got a good parts after that.

Of course, you may have also improperly mixed the first resin batch

Squall67584 · Post by **Squall67584** » Mon Nov 30, 2009 5:59 pm

The molds were a few months old, but were never used before. I'm not sure if Smooth-On's Oomoo is tin-cure or not, but that's what I used. I also didn't do the oven thing as I heard it was dangerous to use the oven for cooking food afterwards... not sure about that but didn't decide to risk it. I've got another set of molds I'm eventually going to use, so I'll plan to have the first batch be useless

The good sets did cure semi clear and I can see a bunch of bubbles inside. But the outer portion is smooth and free of defects, so I'm happy.

USS Atlantis · Post by **USS Atlantis** » Tue Dec 01, 2009 3:06 pm

Squall67584 wrote:The molds were a few months old, but were never used before. I'm not sure if Smooth-On's Oomoo is tin-cure or not, but that's what I used. I also didn't do the oven thing as I heard it was dangerous to use the oven for cooking food afterwards

Do what I did

Invest $15 in a cheap Target toaster oven - used only for modeling

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Using Smooth-Cast 325 Colormatch

Using Smooth-Cast 325 Colormatch

Re: Using Smooth-Cast 325 Colormatch