Arg! Contaminated clay...

[HauntCreations]

Hey

My name is Harold and I'm a sculptor. I have a tumblr that I haven't updated in a while but it's got some of my work on it if you want to take a peek:

I have several sculptures that I've done in chavant hard nsp. Somehow, and I have no idea how, the clay has gotten contaminated. I'm trying to mold it with Mold Star 15 and no matter what it becomes tacky wherever the mold material touches the clay. I've done test after test, sealed it with coat after coat of crystal clear and it's still no good.

The best I can get is a slightly tacky on cure. Then, after I take out the sculpt it cures all the way. I was hoping I could get away with that but it turns out that the cast from the mold needs so much clean up that it's not funny. With most of them I can suck it up and clean up the casting and just make a new mold from that but I have one sculpt that that has a LOT of detail.

I called Smooth-on and asked if there was a less sensitive mold material. He suggested a tin cured material, Mold Max 14NV. I read the technical bulletin and it says that sulfur may inhibit curing. I don't know that sulfur is my problem. Frankly I can't for the life of me figure out what's gotten into the clay that's causing the problem... I'm think I've used this same clay with rebound 25 years ago. Not that that makes any sense. That's a platinum cure silicone too... I'm trying to avoid wasting a ton of money on trial sized kits in order to test them all.

Has anyone been in this situation and how did you get out of it? Is there another mold material I can use besides a silicone? Has anyone tried Artmolds.com latex materials? Maybe a brush on sealer? I think the reason the crystal clear isn't working is that it's not really getting into the nooks and crannies. But it's what the smooth-on tech said was best. I'm surprised he didn't suggest his own SuperSeal...

So frustrated right now and wasting money I don't have

[mangozac]

Hi HauntCreations, welcome to RA! Sorry to hear about the issues you're having

Platinum cure silicone (like the Mold Star) can be very sensitive to contamination, as you've found. The cured characteristics of Tin cure silicone isn't quite as good as platinum, but for cases like this is probably going to be your only option.

I'm confused that the Mold Max 14NV tech bulletin says that it may be inhibited by sulfur: that's traditionally not a problem with tin cure silicones. It's well known that you must avoid sulfur containing clays for platinum cure silicone, not the other way around.

I'd do a small test with the Mold Max. Clays will contain sulfur, not be contaminated by it, so if the clays have been usually fine with the platinum cure silicone then it's possible that the contamination is something else incompatible with the platinum cure.

Keep us posted!

Nice sculpting on your site by the way

[paulson games]

Sulfur is the most common item in clay that inhibits the silicone curing, I've also run into issues with wood resins preventing cure in a platinum based silicone. The stuff I'd ordered from TAP plastic wouldn't cure properly because I used a wooden stick to stir the mix.

I use smooth-on stuff oomoo silicone and I use kleen clay for mounting my parts with, it's discontinued and is sold under a new name now. They claim it's the same formula but I've used and it find that the properties are somewhat different, it may be sulfur free but it is different as it's much less tacky than the older clay. As it never really goes bad you can still pick up original brand of kleen clay on ebay or amazon. I've been using the same 1/4 of a pack for the last 5 years on a regular basis and it's still in good working order.


Sculpting with Fimo works quite well with the different silicones I've tried, it does require firing in an oven but it's at a lot lower temp that traditional fired clays. I've also had good success with molding models created with Apoxie Sculpt. Both of those are a bit less sticky than standard sculpting clay but can hold just as much detail once you get used to working with them. Another positive is that Fimo can be blended with greenstuff to enhance the working properties.

You might be able to seal the outside of your sculpts with layer of primer or a spray on mold release, those might provide enough of a barrier to keep the clay and silicone from reacting with each other but it's hard to say for certain.

[HauntCreations]

I'm confused that the Mold Max 14NV tech bulletin says that it may be inhibited by sulfur: that's traditionally not a problem with tin cure silicones.

Shrug, first page second paragraph of the data sheet


Mold Max® 14NV rubber may be inhibited by sulfur base clays resulting in tackiness at the
pattern interface or a total lack of cure throughout the mold.

I'd do a small test with the Mold Max. Clays will contain sulfur, not be contaminated by it,

Well, I say contaminated by something because what I bought was supposed to be sulfur free clay. IT had a big NSP on the package.

Nice sculpting on your site by the way

Thanks All those sculpts are made from the contaminated clay :-/

The stuff I'd ordered from TAP plastic wouldn't cure properly because I used a wooden stick to stir the mix.

I used a wooden stirring stick but I know it wasn't that. The same silicone cured everywhere else but the surface that touched the clay. Oh, I'vce also called Smooth-on and checked the batch numbers. Both parts A and B are less than 3 months old.

I use kleen clay for mounting my parts with,

I've tried kleen clay for sculpting and didn't like it. It's too soft and mushy. I like a very hard clay to sculpt with, It holds detail better. I ordered a batch of monster clay. It's gotten some good reviews.

Sculpting with Fimo works quite well with the different silicones I've tried,

I've found Fimo difficult to work with. I really liked Chavant. Maybe I'll try another batch if the Monster Clay doesn't work out for me.

You might be able to seal the outside of your sculpts with layer of primer or a spray on mold release,

I've used Crystal Clear to seal the sculptures but it hasn't worked. I might try a brush on sealant of some kind. I don't think the spray is getting into all the nooks and crannies. :-/

I'm probably going to end up trying the mold max. I don't know what else to do...

[HauntCreations]

Just thought I'd update this thread in case someone else runs into the same problem.

I sealed the contaminated clay sculpture with Smooth-on's Super Seal and then a quick coat of crystal clear just for extra safety. The Crystal Clear probably wasn't necessary but I'm not taking any chances at this piont.

Then I made a cavity mold using Smooth-on's Mold Max 14NV and BINGO! Complete cure and a good mold. The mold max doesn't have as long a life as the platinum silicones but, I wasn't left with much choice in this case...

[mangozac]

Thanks for the update! Glad to hear it worked out well! If need be you can always use one of your resin casts to create a new mould in the platinum cure silicone in the future so that it has longer lifespan.