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Monday, October 28, 2013

Day 2 of My Metal Clay Sintering and Kiln Tests

This is a continuation of my metal clay firing schedule tests.  See previous blog entries for more explanation.
After phase one, I didn’t notice the kiln was finished until the temp was already down to 900 degrees, at which point I just opened the lid fully.  About 20 minutes later, I closed the lid and left it until morning.  In the morning, I blew off some of the ash and added the thinnest layer of replacement carbon.  I then set it to a full ramp to 1420 with a hold time of two hours.

As soon as the hold time was finished, I cracked the kiln open and let it cool down to below 1000 degrees, then I opened it all the way and sifted my pieces out.

I did the “sound” test by dropping each piece onto my steel bench block.  They all made different sounds (see video).  I go in order, 2 then 4, 6, 8, and finally 12-cards thick.

Then I did the water test by putting a drop of slightly sudsy water onto each piece.  The 2 and 4-cards thick pieces easily repelled the water.  6 and 8-cards thick repelled the water but it spread out onto the piece rather than staying in one lump drop form as in the 2 and 4-cards thick pieces.  12-cards thick totally absorbed the water.  One side of the 20-cards thick cube absorbed the water, but some of the other sides seemed to repel it.  (See video)

The sound test, the water test, and the bend test (see next) could mean absolutely nothing important.  I am merely sharing with you some of my experiences.  You will read all kinds of different info about metal clay, testing, and sintering.  The thing is, there are also many KINDS of metal clay and they are not created equal.  So I think the most important thing to do is follow the manufacturer's recommendations.  I just happen to like experimenting and since I'm doing kiln testing anyway, I'm throwing in some added experiments.

Next, I took pliers to the pieces and tried to bend them into 90-degree angles. The 12-cards thick piece snapped rather than bending.  

Here’s a close-up of the interior of the 12-cards thick piece.

The cube I sawed in half, but I stopped right before I got to the bottom because I knew that the act of sawing the cube would burnish the interior sides thus making it impossible to tell if the inside was sintered.  As you can see, where I stopped sawing looks similar to the 12-cards thick interior.  Very porous or powdery even.

So my question is: Did the thicker pieces not fully sinter because of something during the binder-burning off stage or because they simple need higher or more heat in the second phase of the firing schedule?  Is it useful or even possible to get the interior of a thick piece of metal clay fully sintered?  Maybe this IS fully sintered.

And what factor to I alter for my next test?

I’m not saying I need to be able to bend metal clay after firing.  Or even that it’s expected to be able to bend.  I just think the more I experiment with what metal clay can and can’t do, I’m working work toward making the strongest product possible.

Next I decided to fold the pieces over completely in half.  The 2 and 4-cards thick pieces took it well.

The 6-cards thick piece cracked where there had already been a crack showing on its surface.  And the 8-cards thick piece cracked in half completely.

The interior of these broken pieces LOOKS powdery, but it’s not.  If I rub it (or burnish it), it shines like metal.  Rubbing vigorously does not dislodge any particles.

I want to compare pieces from different tests to see if the edge color can go any deeper into the interior of the piece.

I forced  the 6-cards thick piece to break in half then I hammered the halves from 6, 8, and 12-cards thick.  They all flattened without any cracking.

So for my next test, I’m going to keep everything the same except I'll raiser the final holding temp.


  1. did you read this? there are links at the bottom of the post to earlier posts on this topic.


  2. Great post! Been looking into sintering myself recently. Thanks for all the info. Great pics!