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Topic: weird spots in clay  (Read 1074 times)
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hello color!
« on: November 04, 2007 10:06:02 PM »


What's the deal with that? The spots were there before I baked it, and baking didn't make them better or worse. They seem to be spread throughout the clay and are resistant to intermixing with the rest of the clay. They are actually quite small - that thing there is 'bout 1 cm wide. But they are quite bothersome!

My best guess is, I've had this clay for about half a year and I don't like to freeze, so while it's been stored in a rather cool place in my apt, it still somehow baked. But I don't know if that ^^ would actually look like what I have, or how it would bake at some tiny random spots and not others. And if that was the case, wouldn't baking make it look all the same? My theory seems to have holes, so I turn to you guys for help!
Diane B.
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GlassAttic --polymer clay "encyclopedia"

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« Reply #1 on: November 05, 2007 08:19:07 AM »

Those spots are probably something called "plaques" (some people also call them "moons").  They happen in polymer clays because of air or humidity inside the clay (often which got there from the way the clay was conditioned), which during the heating process either turns to tiny pockets of steam or air, both of which swell and increase opacity in those spots.

Plaquing happens in all colors of polymer clay but it just isn't visible in the more opaque colors.   So you'll see them a lot in solid translucent clays (but not so much in the "bleached" version by Premo**), and you'll see them less in clays which contain only some translucent (...sometimes it's not obvious at all which colors of a brand will have translucent in them from the factory --those may even be dark colors which look totally opaque...Sculpey III does this a lot).  The colors with translucent will also darken (not brown, just darken) more than other colors as well.

However, usually the plaques aren't visible until the clay is heated, and because they were in your case I'd say that there could have been some areas in the clay you used or the translucent you added that was stiffened for some reason (even partly cured, as you suspect, but from a problem at the factory) and hard to incorporate back into the clay.  I've seen that in SuperSculpey occasionally, but not often in other clays.  (There is also one special FimoSoft color which intentionally has plaques in it, I think to simulate marble or something similar, and sometimes that clay looks a lot like regular translucent when raw or still in the package... is it possible you could have used that??).

**Plaquing is actually desirable when trying to simulate many natural materials (stone, jade, wood, etc.) because those often have different areas of opacity themselves and look more realistic if they aren't just a smooth even color. So the old FimoClassic "Art Translucent" clay was always the "best" for plaquing in those situations as opposed to other translucents or certainly Premo's bleached version... plaques may even be intentionally caused or caused to increase sometimes by conditioning the clay with damp hands.

If you want to read more about plaques, what causes them and what you can do to avoid them, that info is gathered on this page at my site:
(... click on Plaquing...)

If you don't think that was it, tell us more about exactly which brand and color(s) you used (and I assume you're saying that you saw these while they clay was basically untouched and unmanipulated). 


Diane B.
« Last Edit: November 05, 2007 08:40:20 AM by Diane B. » THIS ROCKS   Logged

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(had to move them from YahooPhotos, so many now without captions)
hello color!
« Reply #2 on: November 05, 2007 03:43:34 PM »

It's Sculpey III in Green Apple. I can't see them in the part of the block that I haven't touched (I only conditioned a little more than I was gonna use), or in the ball that I conditioned - until I start squishing it and conditioning it again. I just tried squishing and conditioning it to see how many spots there are, and it's not nearly as many as on my finished piece, so now that I think of it, it's actually more apparent in the baked version than before it was baked. Maybe I was able to see it better before because I was kneading it for a while, so it got super warm. It probably is plaquing. I know I didn't get any translucent in there, so it must've come this way from the factory, esp. since it is Sculpey III.

So... I'll try it again with gloved hands (just in case I was mysteriously sweating) and less conditioning... and if not... I'll just have to do this with Lumina, which I know and love! Cheesy
Diane B.
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« Reply #3 on: November 06, 2007 09:49:27 AM »

I don't think it's necessary to glove your hands unless yours are really sweaty or it's really warm where you are handling the clay, and it's probably more a case of incorporating air while you're conditioning than humidity**.

There are definitely things to avoid while conditioning to prevent as much plaquing as possible though.  If you want to read about those, there are some listed in the category-and-link I posted in my last message, but also much more in:
... click on Bubbles...whether you're using a pasta machine or not
(And the basics re ways to condition clay in general are in:
http://www.glassattic.com/polymer/Conditioning.htm )

(Btw, the "squishing" and "mooshing" methods of conditioning may definitely introduce air into the clay depending on how they're done.)

**if it is humidity that's the problem though, you can get rid of a lot of it simply by letting the clay item sit out overnight before baking  (some of the moisture close to the surface of the clay will migrate up, and evaporate off)

Good luck!

Diane B.

few of my photos
(had to move them from YahooPhotos, so many now without captions)
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