Day 3 of Metal Clay Sintering Testing

As mentioned previously... for my next test, I’m going to keep everything the same except the final holding temp.

Ramp 1                         500°F/hr

Holding Temp 1           1420 for 1 hour

Carbon Under              ½ inch

Carbon Over                ½ inch

Ramp 2                         full

Holding Temp 2           1450 (was previously 1420) for 2 hours

And I’m only doing…

6-cards thick ¾ x 1½ inch rectangle

8-cards thick ¾ x 1½ inch rectangle

12-cards thick ¾ x 1½ inch rectangle

I guess only two things can affect the sintering process.  One, the binder doesn’t burn out properly… or two, there isn’t enough heat to cause sintering.

So if I find out the highest temp I can go without showing signs of over-firing, then I can work on the other factor (making sure my binder burns out completely).

At the end of phase one, I cracked the lid until the temp dropped to 1000, at which point I opened the lid all the way for about 15 minutes.  Then I closed the lid and went to bed.

In the morning, I started phase two.  At the end of phase two, I cracked the lid until the temp dropped to 1000, then I removed my pieces.

Here’s what they look like straight out of the kiln.

I repeated the “sound” test.  All three pieces made metallic sounds.  This 12-cards thick piece made a more metallic sound than the 12-cards thick piece from test 1.

I repeated the “water” test and although the 12-cards thick piece did absorb the water drop, it took about 30 seconds.  As you recall from yesterday’s video of the test 1 pieces, the 12-cards thick water absorption was almost instantaneous.

Just to compare, I flipped the pieces over and did the water test on the backs (the sides that were face down in the kiln).  The water seemed to absorb faster on the backside than on the top side.

Now to bend and break them so I can see what’s inside and compare them to the inside of test 1.

I have mixed feelings about bending.  I want the metal to bend and not break (not sure why) and yet I need it to break so I can see what’s inside.

First I bent them into 90-degree angles.  Not a single crack.

Then I bent them into parallel U shapes.  6 and 8-cards thick were fine.  When I got a small crack on the 12-cards thick piece, I stopped bending it.

Next, I continued to bend the 12-cards thick piece so I could see what the inside looks like.

As you can see, there is no part or edge inside that is thicker (more compacted) than any other part.  That bit on the upper right side of the bottom piece is not a thicker edge as I first thought.  It is where the piece started curving because I bent it.  

The white areas on the upper part are where I ran my fingernail across the inside.  The fact that my fingernail could burnish it rather than finding powder, leads me to believe this is sintered.

Perhaps there is no way to make the interior less porous.

But since these pieces all came out with no signs of over-firing.  I think I’ll repeat the test with a higher phase two temperature so I can find the point that lies just below over-firing.  Although I still assert that it could be a different point for different thicknesses, shapes, and/or combinations of clay. 

Come back tomorrow to see the next results.