Pugaboo Posted October 27, 2014 Report Share Posted October 27, 2014 Can using Pam cause your seams to crack? I haven't really used any kind of mold for making stuff before oh and I am not talking slip casting more like a hump or slump. I found this old green plastic bowl, atrocious color but interesting shape it's round on the bottom but square on the top. I liked the shape so got it brought it home and made a stencil shape from the sides to use as a guide to cut out my clay. I need to add texture to the surface of the clay and it needs to be shaped in a curved manner, etc so I decided to build the form around the outside of the bowl using it like a slump mold. I have heard of Pam being used to "grease" a mold so the clay won't stick to it so sprayed the outside of the bowl with Pam. I built my bowl finished the outside seams, added my texture, firmed it up a bit with my blow dryer and using a piece of drywall flipped the bowl upside down and off the "slump mold". I sprayed the inside of the mold aka plastic bowl with Pam and then carefully settled my clay bowl into it. I added coils of clay to all the seams after scoring and slipping. I smoothed out the seams and even used a pony roller to make sure they were really nicely joined. I sat the bowl aside in the mold until it shrank enough to pull away slightly from the interior edges of the bowl. I then removed it entirely from the mold to dry on its own. The first time I had a problem with the bowl it got through the glaze firing but came out with all these fine cracks on the inside and upon examination it looks to me like the cracks follow the seams and even radiate out from them... As if where I smoothed the coils into the surrounding clay also cracked. The second time I had a problem it didn't even make it to bone dry when upon very close examination I noticed these same fine cracks appearing. The cracks are only on the interior of the bowl not on the exterior at all. Question... Can using Pam contaminate the surrounding clay so that when joining two pieces of clay together they will not meld and blend properly and cause cracks? I am VERY familiar with building boxes, trays with handles, embellishing pieces with other pieces of clay etc and have NEVER lost a piece to cracking until I decided to try and use a mold sprayed with Pam. oh and I didn't use a plastic sheet as I have noticed it can leave creases in the clay if pressed up against it too tightly which inside of a mold would do even more than just wrapping a box to stop the drying. Additional details: Little Loafers cone 6 the bone dry bowl I already tossed into reclaim the fired bowl I could try and get some pics of but the cracks are very fine and the camera might not catch them. Nothing else in the kiln load cracked and I let it cool all the way down Yes I have used the glaze combination before with no issues. No the pieces were not dropped or banged in any way, it's my private studio, and I was extremely careful. Soooo any suggestions why the cracks are appearing when they never have before? Any suggestions on what to use to get the clay to release from the mold? Terry Link to comment Share on other sites More sharing options...
Mark C. Posted October 27, 2014 Report Share Posted October 27, 2014 Pam is an oily substance-not good for connections in clay. How about mold soap from an online store- as far as pam on clay it will burn off-no effects-its not good for plaster but thats not how you are using it. If you are getting it on the seams as you connect them then it acts as a resist. The hairline cracks I have no idea-You could pick up some green soap at the local drug store -that works well as a release as well. Not sure about little loafers-I cannot stand big loafers as lazy folks I stay clear of even little ones. Mark Link to comment Share on other sites More sharing options...
Pres Posted October 27, 2014 Report Share Posted October 27, 2014 I have made some jars where I used "bakers spray" to line the bas relief form to allow the clay to come out of the fine lines and crevices. It worked well, but then I beveled the pieces afterwards to join into a rectangular box form. No problems with joins. The bakers spray worked better than pam that I used first. Link to comment Share on other sites More sharing options...
jammy43 Posted October 27, 2014 Report Share Posted October 27, 2014 Not sure if I'm reading your post correctly, but if you are building on the outside of your bowl, then the clay drying doesn't have the room to shrink, even if its just enough for it to firm up, especially at connection points. Have you tried building from the inside of the form? Mark also has a very good point that the pam is most likely also interfering with joins, another releasing agent is dish soap (not sure how it would effect joins). Link to comment Share on other sites More sharing options...
Mug Posted October 27, 2014 Report Share Posted October 27, 2014 Crush up some of your Little loafers or use some little loafers dry powdered clay run it through an 80 mesh or finer screen. Fire the powder to bisque in a bowl. Put that dust into the center of a piece of old t-shirt material. Wrap up all of the edges, then tie them off with a string, you should now have a pounce bag. Then try using that to pounce your mold with the dust instead of Pam. I would think Pam could interfere with the clay joints and would seal off the plaster preventing the plaster from doing it's job. Try the dust it may be just what you are looking for. Link to comment Share on other sites More sharing options...
Chantay Posted October 27, 2014 Report Share Posted October 27, 2014 I started using corn starch, read about it here on CAD. I works really well. Not sure if it would work on a plastic mold. You could make a plaster mold of the inside or outside of the bowl. Link to comment Share on other sites More sharing options...
oldlady Posted October 27, 2014 Report Share Posted October 27, 2014 mug, she is not using plaster. terry, if you suspect the pam and have tossed the bad bowl into reclaim, toss it into the trash instead. Link to comment Share on other sites More sharing options...
Mug Posted October 27, 2014 Report Share Posted October 27, 2014 OOPs... Dusting may work Link to comment Share on other sites More sharing options...
bciskepottery Posted October 27, 2014 Report Share Posted October 27, 2014 If I'm reading your process correctly, you are putting Pam on the outside of the bowl, making your form over the outside and removing it, then putting Pam on the inside of the bowl and putting your form inside. It appears you are trapping a layer of Pam (from the outside application which would be on the inside of the bowl once you flip it) and then putting coils and slip to seal the inside seams. So, the cracking may be caused by the Pam oils trying to escape or burn out during firing. Usually when Pam or other releasing agents (e.g., WD-40) are applied to a mold, it is on one side only which allows them to evaporate/burn out. Maybe try building the form backwards from how you are doing it now. Build on the inside of the bowl, let it firm up, then remove it and refine the outside. That way, you would only need to apply the Pam to one surface. Link to comment Share on other sites More sharing options...
Pugaboo Posted October 27, 2014 Author Report Share Posted October 27, 2014 Thank you everyone. I will try some of the other methods mentioned. I knew there had to be a better way of doing it than using the nasty Pam spray. Oldlady - thank you for mentioning tossing the bad bowl in reclaim... Good catch .. I picked out the pieces and tossed it in the garbage instead. Terry Link to comment Share on other sites More sharing options...
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