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Topic: How long do you work your clay before curing?  (Read 7589 times)
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yelppuppy
« on: July 06, 2009 10:56:59 AM »

Yesterday I tried polymer clay for the first time, and it's pretty fun.  After all was done, I realized I was subconsciously rushing myself so the clay doesn't dry out before baking.

I know I have more than a few hours before the clay hardens according to Diane B's website, but the exact time frame is unclear (2-3 days? 8-10 days?).  I used Premo and will try FIMO classic and FIMO effects next week.  How long do you usually leave the clay out before baking it?  What's the "cut off" time before you consider baking a portion first as opposed to finish the entire sculpture/project?
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Diane B.
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GlassAttic --polymer clay "encyclopedia"


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« Reply #1 on: July 07, 2009 07:42:24 AM »

Quote
I know I have more than a few hours before the clay hardens according to Diane B's website, but the exact time frame is unclear (2-3 days? 8-10 days?).  What's the "cut off" time before you consider baking a portion first as opposed to finish the entire sculpture/project? . .

LOL... I hope you didn't read quite that at my website!

Actually, since polymer clay is an oil-based clay rather than a water-based clay like most other types of "clay," it will never dry since there is no water in it to dry out (...so, there is no "cut off time").  That's just one of the things that makes polymer clay so cool, and you're in a whole different world in many ways with it.

To get "hard," polymer clay actually has to be heated (to a certain temp, for a certain amount of time), or it must be exposed to a lot of UV light... that's why polymer clay is said to "cure" rather than to dry (heat and UV cause the plasticizers in polymer clay to polymerize, or to form into long chains, which leads to less and less pliability).

What my page was probably referring to is the fact that polymer clay will harden a bit any time it's cool rather than warm (not hot though) --which means after the heat and friction created by hands, manipulation, stretching/conditioning, and environmental conditions have warmed it up, then stopped (or before the clay has been taken out of the package, in which case it will be stiff or soft depending on its brand and age, and even the exact plasticizers available when that bar was manufactured).  We usually refer to polymer clay as "stiffening" though when cool, rather than actually hardening.

Raw polymer clay will stay "conditioned" or more-pliable for awhile, though the longer it sits the stiffer it will get (partly also because the various ingredients will "sink" in the clay, I think, etc, and may eventually need to be mixed up again, or because the clay gets subjected to some heat and/or UV light...all the chemistry is a little more complicated but that's the main stuff you need to know).

Many clayers actually their clay intentionally though at various points so it will be eaiser to work with (not too soft) --for example, before slicing (a cane or loaf, for mokume gane, etc), while working on a sculpt, after a lot of color mixing/etc, when using an especially soft brand of clay, etc.  
Polymer clay can also be "leached" (wicked on something porous) to remove at least some of the plasticizer if a clay is too soft.

If you were on my Conditioning page when you read about that, you might want to read it again now since you'll understand what it means much better! Grin
http://www.glassattic.com/polymer/Conditioning.htm

If you were reading about "partial baking" though or "sculpting," you might have seen some references to those topics on other pages since some clayers do like to partially bake their more complex sculpts (or parts of them) at various points during the sculpting so they won't accidentally smoosh some part they've already finished.  Doing that will polymerize the clay to some extent (at least the part on the surface) which can help, though a few clayers feel that could weaken the clay.

Quote
I used Premo and will try FIMO classic and FIMO effects next week.  How long do you usually leave the clay out before baking it?

Different brands and lines of polymer clay are naturally firmer or softer when raw (depending on their formulas).  All will get firmer or softer in the ways described above, but in general the order of firmness is this--beginning with firmest:
...FimoClassic, Kato Polyclay
...Studio by Sculpey, Premo, FimoSoft (the Fimo Effects colors are in the FimoSoft line), Cernit
...Sculpey III
(Those are the pre-colored clays...the single-color bulk clays also differ in firmness while raw.)
In general too, the softer a raw clay is, the weaker it will be in any thin or projecting places after curing and the more difficulty it will have getting fine detail, not distorting or getting fingerprints, etc. (Sculpey III, Sculpey, and SuperSculpey are the most problematic for weakness and too-softness).

As for how long to leave polymer clay out before baking it, that can vary from immediately to years from now.  
Most people just bake right away but there are some advantages to leaving it out at least a while (even an hour, or overnight for absolute best) since any moisture that's found its way into the clay from hands/air/conditioning/inclusions/etc and even some of the air that might have done the same will have an opportunity to work its way to the surface and get out (which means that moisture or air captured in the oil-based clay won't cause problems inside it when they're expanding from being heated).  Also, the plasticizer around any joined areas will begin to migrate and make those areas stronger.

Here's my page on Baking, if you're interested in much more on that whole subject:
http://www.glassattic.com/polymer/baking.htm


HTH,

Diane B.

« Last Edit: July 07, 2009 08:23:00 AM by Diane B. » THIS ROCKS   Logged

POLYMER CLAY "ENCYCLOPEDIA" 
http://glassattic.com/polymer/contents.htm
few of my photos
http://s96.photobucket.com/albums/l163/DianeBB
(had to move them from YahooPhotos, so many now without captions)
yelppuppy
« Reply #2 on: July 07, 2009 09:42:09 AM »


What my page was probably referring to is the fact that polymer clay will harden a bit any time it's cool.  We usually refer to polymer clay as "stiffening" though when cool, rather than actually hardening.

Sorry, "stiffen" is what I meant.  I know polymer clay can't be air cured LOL! 

I was worried about it getting stiff AFTER i sculpted parts of my sculpture, since at that point i can no longer "massage" the clay to warm it up.  That's why I posted this thread getting a feeling how most other clayers feel about baking parts of the sculpture separately or all in one piece.


Quote
As for how long to leave polymer clay out before baking it, that can vary from immediately to years from now.  
Most people just bake right away but there are some advantages to leaving it out at least a while (even an hour, or overnight for absolute best) since any moisture that's found its way into the clay from hands/air/conditioning/inclusions/etc and even some of the air that might have done the same will have an opportunity to work its way to the surface and get out (which means that moisture or air captured in the oil-based clay won't cause problems inside it when they're expanding from being heated).  Also, the plasticizer around any joined areas will begin to migrate and make those areas stronger.


That's a very good point, Diane.  Thanks!  It's also good to know some leave the clay out for years!  That really gives me a peace of mind as I don't think I'll leave it out for more than 7-10 days given how small my project is.  Grin
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Diane B.
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GlassAttic --polymer clay "encyclopedia"


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« Reply #3 on: July 07, 2009 11:04:05 AM »

Quote
I was worried about it getting stiff AFTER i sculpted parts of my sculpture, since at that point i can no longer "massage" the clay to warm it up.


Well, you can actually massage the clay, as well as warm it or smooth it with one of the other methods on the page I linked to, but it does get more difficult.  Clayers who sculpt have figured out various ways of dealing with that situation though (and most of the info I have on that at my site will be on the Sculpting-Gen page), though the Baking page will deal with "Partial Baking" or multiple baking.  (Info on the Conditioning page about warming the clay could be helpful too.)

Clayers who cane also sometimes need to rewarm canes if they're quite old before slicing them, and older Skinner blend or other sheets may need to be dealt with too.


HTH,

Diane B.

 

« Last Edit: July 07, 2009 11:08:12 AM by Diane B. » THIS ROCKS   Logged

POLYMER CLAY "ENCYCLOPEDIA" 
http://glassattic.com/polymer/contents.htm
few of my photos
http://s96.photobucket.com/albums/l163/DianeBB
(had to move them from YahooPhotos, so many now without captions)
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