Sculpey cracking

RokuroKubi · 02-09-2008, 06:49 AM

Greetings Statue Forum.
New member, new sculpey user.

I've run into some trouble with cracking on my most recent sculpt. I did a bit poking about in the existing threads but didn't come across a definitive answer to my questions, so I hope you won't mind me asking questions that have no doubt been covered in the past.

I sculpted up a small bust with a wire armature. At its thickest point its about an inch thick. I didn't think this would require aluminium foil padding. I baked it at 130C as the box suggests for a bit over 30 minutes. After removing the sculpt from the oven while it was still warm, I noticed a small crack at one of the thicker points.
I left the bust for a day or so and then patched the crack up with some more sculpey along with doing a little refinement to the form. I once again baked it the piece at 130C for 15-20 minutes or so. I removed it from the oven and left it on the bench to cool. Once cooled I checked it over. No cracks.
About a week later I looked over the sculpt again and noticed that a number of quite large cracks had opened up at various points on the bust.
So my qustions are:
What most likely caused this problem? How do I avoid this cracking in future? and How do I go about patching all these nasty cracks without making the situation worse?

Thank you.

riderV3 · 02-09-2008, 04:50 PM

Sounds like you're sculpey layer is too thick, the instruction on the box also says if the sculpt is going to be thicker than an inch, you have to pad the armature with foil.

And try changing your baking temperature to about 200 degree F for an hour instead of 250 for 30 mins, and after baked, leave it in oven for another hour or so to let it cool off slowly and naturally.

Tommy Allison · 02-09-2008, 06:41 PM

Three things cause Sculpey to crack.

Improper baking. I leave my stuff in the oven for an hour and a half.

Another cause of cracking is air trapped inside the foil that expands and contracts.

The last cause is if you've already baked it, and it has cracks, humidity can be absorbed, cause the piece to expand, and when you bake it again it will contract even worse and crack apart.

The best thing for you to do, is bake your sculpt after you've got it the majority of the way finished.

RokuroKubi · 02-09-2008, 10:28 PM

Ok, so it sounds like I'd be best to just put up with the cracks and move on to a new piece rather than trying to fix them, right?

Tommy Allison · 02-10-2008, 12:31 AM

When you're done with your final bake, any cracks you have I'd fill with Apoxie Sculpt.

amusedjester · 02-20-2008, 09:41 PM

Some people leave their pieces in the oven so that it cools down gradually. I am not patient enough for this. The method I use, which I read somewhere, is Immediately after removing from the oven I put the piece in ice cold water with ice and let it sit there for 30 minutes; make sure all of the piece is submerged. Interestingly enough it closes some of the cracks up, as long as they're not gaping cracks. Since you're planning to move on the next piece, why not try it out. BTW, my sculpts have aluminum foil inside to bulk it out, It's by no means solid.

twisterred · 02-20-2008, 09:51 PM

I baked last night a Mindless One figure I am working on, lots of depth to the clay but I poked holes in it to make sure the heat got to the very center. That worked pretty well for me. I did it around the time I was going to bed so that it could rest and go down in temp naturally in the oven and this morning all I had was a really minor crack that will be easy to fill and work over as it isn't deep at all. I also slowly raised the temp in 50 degree incriments at a time after I hit 175 F.

katherla · 02-20-2008, 10:21 PM

I baked one of my sculpts following William's directions from the sticky thread here...

http://www.statueforum.com/showthread.php?t=33465

...and it worked perfectly. I was actually surprised at how dark it came out. I used super sculpey (the pink stuff) and it came out a nice dark brown (like a grilled cheese sandwich).

I did have an armature with some foil padding in the chest, hips, and head.

I work during the day so the six hour bake time wasn't really realistic for me until the weekend. I started it at about 6:00 pm and at midnight I turned off the warm oven and went to bed. The next morning I had a nice, brown, crack-free statue.

Kdawg59 · 02-22-2008, 10:17 AM

Quote:

Originally Posted by katherla

I baked one of my sculpts following William's directions from the sticky thread here...

http://www.statueforum.com/showthread.php?t=33465

...and it worked perfectly.

William would never steer anyone wrong. His particular baking "recipe" and his generosity in sharing in has made a TON of us happy...

I have baked stuff that has well over an inch thickness and using William's technique and sometime perhaps baking it a bit hotter and longer even has given me some well and thouroughly baked pieces... an amazing difference...

Patience is worth it when baking a piece... you spend 10-100 hours sculpting a piece... 6 or seven hours in the oven is a small price to pay I say

Ceramicus · 02-22-2008, 12:22 PM

Mmmmm... grilled cheese sandwhich. I haven't had one of those in eons.

Well, now that the secret to baking sculpey is out, we just have to convince someone to make a kitchen oven that is fully programable for use with baking polymer sculpture clays - i.e. Set X temp for 2 hours, lower to X temp for another hour, etc....You know - Bake while we sleep or "Set it and forget it".

Oh, and it still has to be able to cook up the perfect grilled cheese sandwhich!