Jan 27 2013

One More Discovery

In the previous posting I reported that I had been able to sinter small amounts of copper and Bronze XT in combination with Low Shrinkage Steel XT. Pushing the limits just a little bit further, I tried to fire bigger amounts without pre-firing.

Remember the project “Overlay with Bronze XT? I re-made it with Low-Shrinkage Steel XT. Copper backing is 4 cards thick, each overlay is 4 cards thick.

It worked.

Overlay with Low-Shrinkage Steel XT

Two hours firing, no pre-firing, full sintering. Just like the old silver clay.

And it worked again.

Skyline Ring

And again.


And again.

Another Room

At one point I started to add a copper circle and a Bronze XT circle to the batches. While the copper circle sintered some of the time, the Bronze XT circle did not sinter at all. They sintered only when they were combined with Low-Shrinkage Steel XT in a single piece.

The instruction manual is about to be updated. Except for the new discoveries discussed in the last three postings, other issues will be revisited, such as pre-firing on a stove top vs. pre-firing in the kiln, arranging pieces in the firing vessel, and ramping speed.

Jan 22 2013

Breakthrough in Firing Schedule – Further Tests

Firing with core material at high-fire schedule

Following my recent breakthrough in firing schedules, the next thing I tried was to fire Low-Shrinkage Steel XT in combination with core material – specifically, Creative Paper Clay. My suspicion was that (1) the paper clay might not burn off without pre-firing; (2) the paper clay might interfere with the sintering of the steel.

Here are the fired pieces:

Core Material

Core Material

Core Material

All 3 pieces sintered fully after 2 hours at high-fire schedule with no pre-firing. The paper clay behaved exactly the same as with pre-firing; it turned into dust and buffed away.

The third piece is a combination of Low-Shrinkage Steel XT and Bronze XT. Bronze XT was only 1 card thick (see pp. 107-115 in my book Metal Clay Practice). It sintered just fine.

Increasing ramping speed at high-fire schedule

All my tests are done in a brick kiln. Muffle kilns ramp faster, even if they are set to the same speed. It may have been that in my previous experiment, the steel sintered without pre-firing because it had a lot of ramping time. To rule it out I increased the ramp. Total firing time at high-fire schedule was about 3 hours.

The results are surprising:


Before firing

Before firing

After firing

After firing

1. Low-Shrinkage Steel XT by itself, as well as Low-Shrinkage Steel XT in combination with 2-cards thick copper and bronze XT fully sintered.

2. No cracking occurred as often happens with pre-firing steel clay on a stove top. No repair was necessary.

3. No fireable stones clouded, as they sometimes do, even at lower temperatures.

Firing color-patterned pieces at mid-fire schedule for only one hour

This is something I did not intentionally test, but happened to notice. As you may recall from the previous posting, less than 100 grams of clay can be fired for just one hour after pre-firing. The surface of color-patterned pieces, when fired for only one hour in a batch that weighs less than 100 grams, comes out significantly more flush and smooth than in a 2-hour firing. That makes it much easier to finish.

Color pattern at 1 hour

The Instruction Manual is not updated yet. There are some findings for which I have no explanation just yet, but they seem to imply that further improvements can be done to the firing schedule.

Jan 18 2013

Breakthrough in Firing Schedules

With the encouragement of the participants in my most recent intensive, and with their kind permission to experiment with their pieces, important progress has been achieved in shortening the firing schedule:

Low Shrinkage Steel XT by itself, as well as Low Shrinkage Steel XT combined with small amounts of copper and Bronze XT do not require pre-firing.


Two big rings that were fired in a brick kiln for 90 minutes at high-fire schedule (1700°F/926°C) with no pre-firing came out completely sintered. The total weight of the two pieces together was less than 100 grams. They are not shown here because I have not done any finishing on them. An attempt to fire a group of pieces weighing more than a total of 100 grams required re-firing.

The batch in the photo below was fired for 2 hours with no pre-firing. The weight was a little over 100 grams. (It looks like a lot more than 100 grams, but keep in mind that steel clay is very lightweight.) All sintered fully.


Here are photos of the individual pieces:






Hollow Trapezoid


Hollow forms did not crack at the seams, as sometimes happens when they are pre-fired.

Pieces made of copper and Bronze XT, fired at the same temperature, did not sinter. However, small amounts of these clays did sinter when added to steel pieces.







The overlays were rolled 2 cards thick before sanding. All sintered perfectly.

The second experiment was done at mid-fire schedule. After pre-firing, 100 grams of copper, bronze, and Brilliant Bronze were fired for only one hour. All sintered. A batch of 10 big rings only sintered partially. My theory is that the bigger the total amount of metal fired, the more time is required for the heat to reach all of it. What supports this theory is that all repairs, fired for 1 hour with no pre-firing, were successful.

To sum up:

1. Low-Shrinkage Steel XT by itself, as well as Low-Shrinkage Steel XT combined with small amounts of Quick-fire copper and Bronze XT, can be fired for 2 hours at high-fire schedule with no pre-firing.

2. Up to 100 grams in total of Quick-fire copper, bronze and Brilliant Bronze can be fired for 1 hour at mid-fire schedule after pre-firing.

3. Repairs for any of the clays can be done with no pre-firing for 1 hour only.

I am not updating the instruction Manual just yet, since I plan to continue experimenting. Hopefully, more results will be posted soon.

Jan 13 2013

Another Project for the ClayMill Extruder – Part III

The ClayMill Extruder comes with 5 dies. What is the serrated (zigzag) slot for?

One technique in traditional Damascus steel and mokume-gane is to emboss the layered sheets of metals (the billet) to about a third of their thickness and then file off the raised parts to reveal the pattern. The die with the serrated slot mimics this technique. There are major differences, though:

1. In traditional Damascus steel and mokume-gane several sheets of different metals are layered one on top of the other. Therefore, when embossing into the same depth at different spots of the billet, the same pattern will be exposed. This can easily be illustrated by stacking layers of polymer clay instead of sheet metal, embossing the stack with a V-shape wood carver, then removing the raised part. The extruder produces a cane, or a stack, that consists of layers of different clays. However, they are not arranged one on top of the other; when embossing into the same depth in different spots of the cane, different patterns of color will be exposed. The pattern will always change along the cane.

2. In traditional Damscus steel and mokume-gane the billet is created first and then the embossing is done. The extruder, in combination with the serrated slot, does both at the same time: it extrudes a cane that is indented to almost a third of its thickness by the sharp edges of the slot. Then the raised parts are removed to reveal a pattern of color.

Here is a project, entitled Color-patterned Hair Band, which illustrates this technique.

Hair band

Materials: Quick-fire copper, Quick-fire bronze, Quick-fire steel (any kind).

1. Place the die with the serrated slot in the cap of the extruder.

Serrated die in cap

2. Make a stack of alternating circles: 2 copper (6 cards thick), 2 bronze (3 cards thick), and 2 steel (1 card thick). This stack weighs about 80 grams, including the water. Use a circle cutter about 1¾” in diameter. The diameter should be just slightly bigger than the slot.

Stack of alternating circles

3. Extrude the stack with the copper circle coming out of the slot first.

Stack extruded

4. Using a craft knife or a tissue blade, remove the high parts of the cane. It is not necessary to create a perfectly flat layer since some sanding will be done later.

Remove the high parts

5. Using craft sticks, correct any distortion by shaping the cane into a rectangle.

6. If you wish the rectangle to be longer, roll it down between the two craft sticks.


7. Curve the cane on a cylinder-shaped mold such as a dowel, and dry.

Curve the cane

8. Sand the surface smooth to reveal the color pattern.

Sand smooth

9. Make the stick: roll a thick copper snake. Place the piece on top of it to measure the length, and cut it so that it protrudes past the shape by about ½” on
each side.

Make the stick

10. Press on one end with your finger to flatten it. Dry and sand it to the desired shape.


11. Drill a hole on each side of the hair band. Make sure the holes are big enough for the stick to fit through.

Make a hole


Stick fits through

12. Fire the band at mid-fire schedule. Fire the stick at high-fire schedule. Follow the firing schedules in the Instruction Manual (also available in the right-hand pane of this blog).

13. Finish the piece following the instructions in the document entitled “Finishing Fired Metal Clay” on my blog (also available in the right-hand pane of this blog).

Jan 9 2013

Free Project for the ClayMill Extruder – Part II

As promised at the very bottom of my earlier posting, here is the project for the ClayMill extruder, entitled “Cat’s Eye Ladder.” To view or download the project as a PDF document, click here.

Jan 2 2013

Tips for Using the ClayMill Extruder:
Part I

If you haven’t taken the ClayMill extruder from PMC Connection out of the box yet, or if you have but were afraid to use it, here are a few pointers that may make it easier for you to get started.

This extruder is quite different from the popular small one. First, It has a black ball at the end of the handle to prevent the handle from sliding off.

Black ball

It’s important to know that this ball screws in reverse (to the right). The reason is, that if it screwed to the left, it would come loose and fall off during the extrusion. So if it seems hard to turn, it is because you are turning it in the wrong direction.

Second, the piston is not attached to the screw. If you scroll the handle all the way to the right, the piston will come out of the barrel.



This makes it easy to clean both the piston and the inside of the barrel.

To put the piston back in the barrel, scroll the handle to the left to make room for it, and place it inside with the circular indentation facing the barrel, and the flat side facing out. Once it’s in, keep scrolling the handle to the left to make room for the clay. Since the piston is not attached to the screw, it will not go in. Simply push it inside with your fingers until it reaches the end of the screw. Repeat this if you need to make more room for clay.


Third, the tube adapter is a disc with 7 holes. It is used with another die, with the thicker rubber washer sandwiched between them (the thinner rubber washer that cones with the kit is a replacement for the washer that is wrapped around the piston). Because of the size of this extruder, it does not necessarily require a pin or a hole corer to create a tube. For example, if you fit the rubber washer between the tube adapter and a disc with a square hole, a square tube with a square hole will be extruded.

Square tube, square hole

Likewise, if you use a disc with a triangular hole, a triangular tube with a triangular hole will be extruded. This is what makes it possible to make the earrings below:


Triangular tubes

Hopefully, more dies with other shapes will be coming soon.

The center hole allows you to attach different sizes of pins or hole corers. The holes will always be round. The type of corers that can be used are shown on p. 116-117 of my book Metal Clay Practice.

The rubber washer that comes with the kit is less than 2″ in diameter. This may cause clay to be trapped between the washer and the walls of the barrel. You can get a larger 5 mm washer at the hardware store for about 50 cents.

When using the extruder with more than one type of metal clay to achieve a color pattern, the steel circle should always be 1 card thick, or it will not be able to sinter. If the mix involves bronze, it means that the piece has to be fired at mid-fire schedule, lower than what is required for steel. Only minimal amounts of steel will be able to sinter at this lower temperature. I often watch students while they work and notice that their steel circle is too thick. “But I rolled it with one card!” is usually the answer. Then I take the roller and roll the circle again, pressing harder. Here is the result:

Original circle

Original circle

Circle rolled again

Circle rolled again

New circle

New circle

Some of us, including me, don’t have enough strength to turn the handle all the way without leaving some clay inside the barrel. I find it much easier to operate the extruder when it is held in a vise.


My suggestion is to first practice the different options with a single type of clay. That way you will not be losing any clay. Anything can be retrieved or recycled.

You will notice that when you use the tube adapter, some clay will be trapped inside the rubber washer. The same happens with the smaller extruder, but with the ClayMill the amount is much bigger. When using a single type of clay, this is not a problem; just return it to your storage. When using more than one type of clay, this trapped clay is still usable. One option is described on p. 119 of the book Metal Clay Practice. Another option will be suggested in part II of this posting, which is a project for a Cat’s Eye Ladder.

Cat's Eye Ladder