Saturday, March 9, 2013

Daffodil Spring Cat and Eliminating the Bumpies when curing Polymer Clay

Introducing Daffodil Cat, the newest member of my Cat Collection who was inspired by the gorgeous blooming daffodils in our garden. When daffodils bloom can spring be far behind?
Entire Daffodil Cat Collection is now available at MelodyODesigns at Etsy
The daffodils in our garden that inspired me thriving beneath the Palo Verde tree
Bumpies, they have various innocuous names, but I call them the BUMPIES!#%^&*?!*. They are the small bumps that appear on the surface of raw polymer clay that are much more visible once the clay is cured. Bumpies are caused by tiny air bubbles that are trapped within the clay. The air can inadvertently become trapped when conditioning with a pasta machine, so it's wise to place the folded end into the rollers first. The cats I make require a sheet of FLAT clay without imperfections and when "cat acne" appears on a piece I'm making for sale it's VERY noticeable and is banished to the garbage can. I normally use PREMO clay, but there are some colors where I prefer to use Kato clay. In spite of taking care in conditioning I've found that no matter how much I've tried to prevent them, I get about 95% more bumpies when I use Kato brand than when I use PREMO.

I recently tried staircase or ramp curing, as recommended by both Jana Benzon Roberts and Tony Aquino (the chemist at Van Aken, the company which manufactures Kato) and I've found it very helpful. One puts the clay piece in a cold oven and cures at the lowest temperature for 20 minutes and then raises the temperature to 200 F for 20 minutes. Then, without opening the oven gradually increase the temperature 50 degrees every 10 minutes until the target temperature is reached and start timing of the actual curing time. For me, ramp curing seems to help a lot with PREMO, but not so much with Kato. I've seen an increase in the problem with both PREMO and Kato since they changed their formulas and I've noticed it's worse with mushy clay that needs leaching.

When I first encountered the problem, about 3 years ago, I contacted Tony. He suggested a "work around", but at the time it wasn't  practical to use it with my designs. This week, when my newly designed Daffodil Cats began sporting roaring cases of acne, I knew I'd either have to find a solution or discontinue using Kato, even if it meant changing my design. I am pleased to direct your attention to the Daffodil Angel Cat hanging ornament below. Look ma, no acne!
Daffodil Angel Cat Hanging ornament
So what did Tony suggest? It's really rather simple, but I think it's only practical to use with FLAT clay designs, like one might make from a flat clay sheet using a cookie cutter. I'm going to paraphrase his burnishing method of eliminating Bumpies adding my own suggestions to his. It seems to work even for clay sheets that were made from bits and scrap pieces flattened together in a pasta machine, a process notorious for producing Bumpies.

The following temperature recommendation and timing are for a piece of Kato clay that is the thickness of #1 Atlas or #5 D.R.E.A.M. pasta machine, roughly 1/8" (3.1mm) and must be adjusted according to the manufacturer's recommendations when using other brands and thicknesses.

Condition the clay any way you like. You don't even have to be TOTALLY meticulous about not introducing air into the clay, though it's a good idea.  Place your flat clay item on a piece of regular copy paper sitting on a ceramic tile, ideally cut to size. Place a slightly larger piece of paper on top of the clay item. Using your fingers, gently burnish the paper onto the top surface of the clay. If you rub too hard you risk distorting the shape of the clay. If you rub too little the paper won't totally adhere to the clay. Place in a pre-heated oven at 300 F for 30 minutes. 15 minutes into the curing time remove the paper from the top surface (careful, HOT!) and finish curing for the remaining 15 minutes. Once the piece comes out of the oven release it from the paper on the bottom (careful, HOT!)so that it doesn't curl as it cools.

According to Tony, "What is occurring is the paper is suppressing the ascent of the rising air bubbles and creating a detour. If there's not an outlet for it, it will not rise above the surface. It also mattes down the sheen, but sanding and buffing will provide an excellent gloss." I have found that using laser paper, which has a smoother surface than regular printer/copy paper lessens the matte occurrence and allows more of the characteristic Kato gloss to show without my having to take the time to sand and buff.
Daffodil Cat worn as brooch
Does the Burnishing Curing Method also work to prevent "Moonies", those light colored crescent shaped imperfections that are also caused by trapped air bubbles?  I don't know because I don't seem to get Moonies, but I would think it might. I'd love to hear from any readers who might try it for Moonies.
Readers tell me they enjoy seeing studio photos, so........
here is a photo of some of the various components that go into the making of the Daffodil Cats
EDITED UPDATE: Yesterday as I was "test driving" my new Daffodil Cat necklace by wearing it with a heavy winter sweater I thought, "Wouldn't it be nice if I could make a necklace variation that had a substantial beaded chain?" I had recently received a large order of colorful 8mm smooth round acrylic beads from Pedazos at Etsy and was thrilled to find I had PERFECT color matches already in my stash. I wore it this morning for the first time and I absolutely LOVE these colors together. There's something so optimistic and sunny about French Blue and bright yellow together.


  1. I love your Daffodil Kitty! It's always great when I see the Daffodils begin to dot the landscape, so bright and pretty, after the long winter!! What a sweet picture of spring you Daffodil Cats are!

  2. Thank you for sharing all this great info for curing 'bumpies'!!

  3. Your daffodil kitty is wonderful! My favorite colors...

    And the solution for the bumpies sounds very do-able!

  4. Thank you for the great information. I love the blue kitty. I can never tell if it's spring in Arizona or not. Seems like it goes from winter to summer and then from summer to winter and we don't get spring or fall.

    I bake most of my pieces upside down so if there are bubbles, they come up on the back side of the piece and you can re-cover them with something or sand and buff. Another thing is, I don't bake my Premo at 275. I put it in a cold oven that I never set at higher that 260. I use to do the same with Kato but I had to quit using that because of the smell.

    Thank you for the nice comment you left on my blog. I think Buster is going to be the size of a little horse. He likes donuts.

  5. Wonderful! I liked reading about how to keep cat acne from appearing, hmmm, too bad it won't work on people! LOL. I'm so jealous that you already have daffodils! Ours probably won't arise from beneath the snow until May. But I'll take photos when they do, for sure. Love your bright kitty, as always.

  6. Great idea! I'll have to give it a try. Sounds like a good way to bake the less textured versions of my switch plate cover designs.

  7. Very informative post, thanks for sharing! Your "daffy" cat is darling!

  8. Very nice design, Anita. I love the colors and this certainly is a great addition to your kitty line.

  9. Here's another idea for help with the bumpies. I do this with Premo (haven't tried it with Kato). When baking flat pieces, I put the flat piece on paper, index card, etc. on a small ceramic tile. Then I put another piece of paper on top and another small tile on top. Then flip the whole thing upside down and cure it that way.

  10. Having just encountered several Bumpies in yesterday's work, I would this really helpful and timely. Thought it was just me....