Mar 31 2010

White Bronze Clay is Now Available

Hadar’s Clay™ – White Bronze is now available on my online store.

You can find the instruction manual on the right-hand pane of this blog and on the White Bronze product page in the store. Please download the instruction manual before you begin firing, since White Bronze behaves somewhat differently from copper and bronze clay. As with all other manuals, the White Bronze manual will be updated on a regular basis. The date of the last update appears at the top of the first page.

Copper clay has a wide range of sintering temperatures, while bronze has a narrower range; White Bronze has a very narrow range. A change of 10°F can determine whether a piece is not sintered or melts. Since kilns are so different from each other, it is important that you find the right firing schedule in your own kiln.

I tested the firing schedule in a top loader and a front loader kiln. The results are reflected in the firing schedule suggested in the manual. Please regard these temperatures as a starting point to determine your own firing schedule. I do not recommend firing actual pieces before firing test pieces. The instruction manual explains how to use test pieces.

White bronze fires when tucked deep in carbon, with slow ramping to a relatively low temperature, and 2:30 hours of hold time.

What can’t you do with White Bronze?

You cannot tell a customer that it’s silver (just kidding, it wouldn’t cross your mind).

You cannot fire it with a torch. The firing temperature is low and the firing time is long (2:30 hours).

You cannot combine it with copper and bronze clay unless the copper and bronze have been fired first.

You cannot bend or hammer it after it’s been fired. Although it’s very hard after firing, it is not flexible at all.

What can you do with White Bronze?

You can make big, chunky pieces that look like silver without feeling guilty.

t-WB rigatoni

t-Next to a penny

t-9-tile pendant

t-Doormat Bracelet

You can combine White Bronze with copper and bronze in the same piece, without having undesirable reactions as between silver and bronze.

t-Oval bead earrings

Unlike silver, you can inlay White Bronze in copper and/or bronze after they have been fired, and they will fuse without separating.

t-Squares

t-Ball earrings

t-Drum earrings

t-Oval bead earrong


Mar 24 2010

Improving Your Torch-firing Results

This is in response to comments by Dragonlady and Jenny on my previous posting.

Whether working in silver or copper, I myself am not a big fan of torch-firing for anything that might have a structural role in a jewelry piece. However, here is another suggestion for improving your results.

When we fire with a torch, we waste most of the heat on heating the air. You can build a “mini kiln” out of a firing surface and kiln posts.

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The posts can be 2-3 inches tall, and, as you can see from the photo, they are arranged in a circular structure, leaving just one opening for the torch.

You can cover this structure with another firing surface, a tile, or a piece of fiber blanket.

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I guess that lining the firing surface with carbon is even better, if you can manage to keep it in place.

Fiber blanket is an excelent heat insulator. Actually, you can replace this whole structure with a cylinder made out of fiber blanket.

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The blanket is stitched with nickel-chromium wire, which resists very high temperatures. In fact, I use it to stitch my fiber blanket boxes, and make eyelets of it to insert into steel clay. Just Google “nichrome” or “nickel-chromium wire.”

Then seal the top of the cylinder with another piece of fiber blanket, and cut a hole for inserting the torch.

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Again, lining the bottom with carbon can’t hurt. I’ll be glad to hear about your results.


Mar 22 2010

Understanding Metal Clay and the Firing Process

When I started my blog, I predicted that within a year many brands of metal clay would be available. This has become true, and it seems to create a lot of confusion. Different sets of instructions have become available, along with different firing schedules, etc. Teachers tend to vary in their choice of brand and may not be fully aware of how to handle other brands.

To help clear up this confusion, I thought it might be best not necessarily to clarify the differences between the brands, but rather to establish what they have in common. My hope is that by gaining an understanding of how metal powder sinters, individual users may find it easier to arrive at their own optimal firing schedule.

I am by no means a scientist. Everything I am about to write is based on a lot of reading, as well as on my personal experience. I have found that reading material about the theory of sintering may not necessarily be helpful, since practice rarely goes hand in hand with theory. However, things that I have read have given me ideas of what may be worth trying, and through trial and error I have arrived at a certain level of understanding. That is all I have to share.

Sintering means the bonding of loose particles together below their melting point. The term sintering applies not only to metal powder but also to ceramics.

Perhaps a good example of sintering is ice cubes. Ice melts at 32°F/0°C. The temperature in the freezer is way below that. What happens if we raise this temperature without reaching the melting point? The ice cubes will start sticking to each other until we are able to pick them up as one solid unit. However, since they don’t touch each other at every point of their surface, there are spaces between them and this whole mass is porous.

The sintering process consists of 2 main phases:

1.Removal of the binder
2.Densification of the particles

The Binder

The role of the binder is to give the metal powder the consistency of clay, so we can shape it or press it into molds. For the clay to turn into pure metal, the binder needs to be removed completely before the sintering process begins. If it is not completely removed, whatever is left of it prevents the metal particles from adhering to each other.

If the binder is completely removed, it does not matter what type it is. The type may affect the working condition of the clay but not the sintering results.

Densification

Once the binder is removed, the particles are allowed to get closer and closer. As far as I know, the particle shape of most metal powder used for the different brands of metal clay is spherical. The spheres get closer and closer, their contact areas grow, but since they don’t reach their melting point and they don’t turn into liquid, they don’t lose their shape completely and there are still spaces between them.

Here is a link to a short video clip that I posted on my blog a while ago. About halfway through the clip you can see a good illustration of it.

http://artinsilver.com/blog/2009/03/08/powder-metallurgy/

So what needs to happen in order for us to have a successful firing?

Precious metals such as pure silver and gold are fired exposed to air. They don’t react with the oxygen in the air, and the oxygen ensures the complete removal of the binder.

Base metal clays such as copper and bronze, when fired exposed to air, react with oxygen to create oxides, which, like the residue of the binder, prevent the particles from bonding. Pure copper can be fired exposed to air for a very short time before it oxidizes internally. However, longer or repeated exposure to heat and air will enhance the oxidation and eventually the copper will disintegrate. This is true not only for copper clay but also to solid copper, such as plumbing pipes and sheets.

Copper alloys, such as bronze, cannot be fired exposed to air. If they do, a large chunk of them will come off, taking with it the texture and details.

So, base metals are fired buried in activated carbon, which reduces the amount of oxygen in the kiln and inhibits this reaction. Gold granulation is done this way since it involves the use of copper. The carbon creates a “reducing atmosphere” by burning; while burning, it consumes the oxygen present in the kiln chamber.

However, most organic binders used in metal clays need oxygen to burn off. If there is not enough oxygen (because it has been reduced by the carbon), the binder will not burn off completely. If the binder is not completely removed, there will be no proper sintering.

So in a way, the activated carbon is both a blessing and a curse. On the one hand it enables sintering; on the other it interferes with the removal of the binder. In industry, vacuum or gasses are used to create a reducing atmosphere.

If we manage to burn the binder before the carbon catches fire, we increase our chances of successful sintering.

From my experience, the binder burns at around 1000°F/538°C in a top loader kiln or 1100°F/593°C in a front loader kiln (I refer to the most popular kilns, that are about 8″x 8″ x 8″). At this temperature the carbon does not burn yet. Some brands of clay have more binder in them than others and may require staying at this temperature for a certain amount of time for the binder to burn off completely.

If you have problems sintering your clay, no matter which brand you use, it is always a good idea to hold at this temperature between 30 to 60 minutes before going on to the goal temperature. Large and thick pieces have a lot of binder to burn, so holding at this temperature will always be helpful. Holding at this temperature will not affect thin or small pieces that may be present in the batch.

Firing Time

The amount of carbon in the box will determine the firing time. The more carbon present, the more time it takes for the binder to burn. Thin and small pieces require very little carbon (1″ below and on top) and can be fired for 1:00 hour once the carbon is removed. In this case, no hold time at 1000°F/538°C or 1100°F/593°C. Thick and large pieces require more carbon and therefore more time, usually 2:00 hours. As I said before, holding at 1000°F/538°C or 1100°F/593°C can only help.

Firing Temperature

Copper clay has a wide range of sintering temperature. If you fire copper alone (preferably in carbon), you can go up to 1800°F/980°C and fire for 1:00 hour.

Bronze will swell and warp if you fire it at over 1470°F/800°C (top loader) or
1550°/843°C (front loader). It is ok to fire copper at this temperature.

White bronze will swell and warp above 1200°F/648°C (top loader) or 1280°F/693°C (front loader).

These temperatures are not absolute numbers. They depend on the size, age, and condition of your kiln, and tests are required before determining your individual firing schedule.

The best test would be to fire bronze or white bronze clay at the suggested temperatures. If the pieces snap at these temperature you need to increase it. If they swell or curl you need to reduce it.

Other Tips

  • The smaller the kiln, the better. Otherwise you are wasting energy on heating air. (Lower temperatures than suggested may be required, though).
  • Use a firing box that is not made out of a poor conductor of heat, such as stainless steel. Stainless steel also oxidizes during firing and contaminates your kiln. I find a fiber blanket box or just a kiln shelf surrounded with kiln posts very effective.
  • Make sure there is some space under and above the box to allow heat flow.
  • Make sure the kiln is vented. The binder, fumes, and contaminants need to escape. If they don’t, they are most likely to inhibit sintering. If you don’t have a venting hole, you can either drill one or fire with the door a crack open.
  • For the same reason, don’t use a lid. The carbon will stay contained in the box and will not contaminate your kiln.
  • Use coconut shell carbon, acid washed, size 12 x 40.
  • After every firing, clean the carbon from the ash that has been generated while it was burning. This way you can re-use it.
  • Unless absolutely necessary, it is best to fire in carbon, starting with a cold kiln and finishing in a cold kiln. Taking pieces out hot may cause oxidation.

This file will be updated as necessary and is downloadable as a PDF file from the right-hand pane of my blog.


Mar 16 2010

Introducing White Bronze – Continued

Here is a report on my further testing of White Bronze clay.

1. I’ve been asked how White Bronze reacts to patina. You can see the result in the photo below.

t-patina

2. How well does it pick up textures? I tried to make my Collage of Textures pendant (first project in the my first book) with White Bronze. It reacts well with liver of sulfur and seems to pick up textures very well.

Before Firing

Before Firing

After Firing

After Firing

3. Smooth/matte/satin finish. Achieving these finishes was no harder than with silver, copper or bronze clay.

t-Earrings2

4. Combining copper with White Bronze.

t-WB in copper

t-Rock

t-2 tone rock

5. Reaction with bronze. I fired both bronze and White Bronze on a copper piece, without sealing the bronze as I would have done with silver. Both sintered, and there was no alloying or change in color.

t-Compatibility with bronze

The following bead has been waiting for this moment for about two years. I fired the copper and the bronze with the intention of adding silver to the bottom part. It was just then that I found out about the reaction of silver and bronze (you can read all about it in my second book), so I stopped working on the bead.

t-3-tone bead

t-3-tone rock

6. Sticking to copper and bronze. Since the firing temperature of copper and bronze is higher than that of White Bronze, copper and bronze need to be fired first. I placed an unfired piece of White Bronze on a fired piece of copper and a fired piece of bronze, and re-fired.

t-Sticking

The results were inconsistent. I repeated it a few times and sometimes they stuck, sometimes they didn’t, regardless of whether it was copper or bronze. My guess is that they will stick if there is a way of creating some pressure between them. The following test supports this hunch. It seems that the pressure of the carbon on the piece was not enough.

7. Inlay.

White bronze in copper

White Bronze in copper

White bronze in bronze

White Bronze in bronze

The following photo shows side by side inlay of White Bronze in copper (R) and inlay of copper in bronze (L).

Color comparison

Color comparison

As you can see, the contrast between bronze and White Bronze doesn’t seem very sharp. Over time it may improve when the bronze yellows some more. White Bronze has not changed in color so far.

The inlay pieces above were only partially successful. In the center of the pieces the metals bonded well with each other. On the peripheries some of the inlay chipped off and required repair and re-firing. It seems that on the peripheries the pressure is lower than in the center.

In the following piece I avoided inlaying the White Bronze on the borders of the piece. The bonding was fine.

t-Inlay


Mar 14 2010

Introducing Hadar’s Clay™ – White Bronze

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The pieces in the photos above (click to enlarge) are not made out of silver or steel. They are made out of a new copper alloy that I call “White Bronze.” This new form of Hadar’s Clay will soon be available for sale on my Web store.

Here is how the pieces looked before firing:

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I have prepared samples of Quick-fire Copper, Quick-fire Bronze, and White Bronze, textured and non-textured.

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The following photo is taken next to a silver piece that may be familiar to you as a project from my first book.

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Here are some process photos:

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Textured and folded

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Dried

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Fired

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Next, some pieces in copper and bronze. Unlike the copper and bronze pieces, the White Bronze piece was textured before folding. When White Bronze is not textured, it comes out as smooth as copper and bronze.

White Bronze is compatible with both copper and bronze; there is no undesirable reaction between them as there is between silver and bronze.

The firing temperature of White Bronze clay is a lot lower than that of bronze clay, though. So in order to make combination pieces of either copper and White Bronze or bronze and white bronze, the copper and bronze parts have to be fired first.

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White Bronze was wrapped around fired copper, then fired.

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The result is the piece on the left. On the right you can see the same piece with silver substituted for the White Bronze.

There are still some tests that need to be done. For example, I need to determine the extent to which White Bronze clay sticks to copper and bronze. I will post my results soon.

As you can see from the photos, the shrinkage rate is similar to that of Quick-fire Copper and Bronze. The firing time is about the same and the temperature is lower. The fired pieces are as strong as those of copper and bronze.

Important Note: This is not “nickel silver” (also known as “white copper,” “German silver,” or “alpaca”). This alloy contains no nickel.

White Bronze clay will be available on my store as soon as I complete my testing and write an instruction manual. I hope you like this low-cost addition to the palette of metal clays.


Mar 12 2010

Podcast

A few weeks ago I was interviewed by Alison Lee, host of Craftcast. A conversation with Alison was published in the March Issue of Art Jewlery Magazine, the same issue that has the article about Shibuichi. If you would like to listen to my interview with her, please click below:

Play Podcast

Play Podcast


Mar 2 2010

Which Carbon to Use?

Although some coal-based carbons are suitable for firing copper and bronze, I have recently decided to stick to coconut-shell carbon. For some time I had not been able to get a good contrast between the copper and the bronze in mixed pieces. This can happen for two main reasons:

1. Over-sanding prior to firing (this could cause particles from each metal to “bleed” into the other);
2. Oxidation of the copper in the process of firing.

I knew it wasn’t the first reason. Something was causing oxidation. After ruling out other possibilities, I replaced my coal carbon with coconut-shell. The differences were striking. Here is how the pieces looked straight from the kiln. I used my new firing method, 1:00 hour at 1450ºF in a fiber blanket box.

t-Straight from the kiln

Another great advantage to coconut-shell carbon is that although I used very little carbon, very little ash was created. I was easily able to vacuum the ash and re-use the same carbon over and over.

The carbon is coconut-shell, acid washed, size 12 x 40.

Bear in mind that probably not all coconut-shell carbons are the same. Different vendors may be supplying different brands. Moreover, vendors change their own suppliers and you may be getting a different brand even if you ordered from your regular vendor. It has happened to me more than once that I was working with one supplier, being quite happy with the carbon, and then the next shipment wouldn’t work anymore.

So I suggest ordering small amounts and testing them. I can’t afford to buy from every possible supplier and test, but I would be happy to test for you if you send me samples.

t-Bracelet


Mar 2 2010

Starting and Finishing Firing in a Hot Kiln

Sometimes, in a classroom situation, we have no choice but to fire one batch after another without letting the kiln cool down between firings. Is this really a good idea?

If you are firing just copper without carbon (“open shelf”), it is not only a good idea but the only option. If you fire copper from cold without carbon, the oxidation layer will be very hard to remove. Moreover, internal oxidation may occur, which eventually may cause the copper to disintegrate.

(A little side note: it is not a good idea to fire copper without carbon, in a kiln or with a torch, more than once or twice. Eventually it will weaken and disintegrate. This happens not only to copper clay but also to pre-made copper sheet and tubing.)

However, if you are firing in carbon, whether copper or bronze, it is better to start in a cold kiln. The binder must burn off before the carbon is set on fire and starts consuming the oxygen in the kiln chamber. If you load the kiln at a temperature between 500°F – 1000°F, the binder has a very slight chance of burning, since it needs oxygen to burn. This will result in poor sintering or none at all. I learned this the hard way.

Is is a better idea to take pieces out of a hot kiln or let them cool down first?

Again, in a classroom situation there is sometimes no choice. But then cool the pieces immediately in water (unless they include stones). Otherwise, the exposure to heat and air will cause oxidation. The time spent on removing the fire scale may be better spent on waiting for the kiln to cool down to about 300°F.

Whether you fire small pieces for one hour in a fiber blanket box, or bigger pieces with more carbon for 2 hours, no oxidation will occur if you just let the pieces cool down before retrieving them from the kiln.