Feb 12 2010

Removing Fire Scale

The shortened firing schedules of Quick-fire copper and bronze clay may result in some fire scale, especially if pieces are not taken out of the kiln as soon as the firing is over. The reason is that by the end of the firing there is not enough carbon to protect them from oxidizing. This oxidizing is external and does not compromise the strength of the pieces, but sometimes it can be hard to remove by just buffing or sanding.

One way to avoid this is to take the pieces out of the kiln when they are hot and cool them in water. By “hot” I mean that you can absolutely wait for the kiln to cool down to about 900°F before you do that.

But if fire scale does occur, there are a few easy ways to remove it. Personally I don’t like to use pickle, but if you want to, a very mild and effective one is citric acid. (Citric acid is actually used to make pickles and exists in many food products and almost every soft drink, as well as naturally in the juice of citrus fruits.) You can get it at Mediterranean food stores. It’s also available at wine-making and beer-making supply stores, as well as at some supermarkets. It’s very inexpensive.

Here are two alternative methods that I prefer:

1. If a piece is small enough, you can heat it with a torch to red hot and immediately quench in water. The fire scale will disappear.

If you choose to do this, there are two things to keep in mind:

a. It is not recommended to do this with pieces that were fired by the “hot firing” method (in the air). It is also not recommended to repeat it more than twice or so since the copper is weakened by air firing and will eventually disintegrate.

b. After dipping in water, the piece must be completely dried on a warmer before you handle it any further. If you try to buff or sand a wet piece, you will not see metallic color and you may think that it is not properly sintered. It is not enough to dry it with a paper towel; the metal is porous and holds a lot of liquid inside, even if it looks dry on the outside.

2. Put the pieces back in the carbon. Heat the kiln to 1000°F and hold for 15-30 minutes. You can take them out hot or cold. The fire scale will be gone. This time there will be very little ash and there is no need to discard the carbon.

Out of the carbon

This piece was taken out of the carbon hot after re-firing for 15 minutes at 1000°F and cooled in water. The fire scale disappeared completely from the copper part.

I used a coarse mini-fiber wheel to clean up the steel part. It was quite easy.

Clean-up with coarse mini-fiber wheel

With the spinner bead, I waited for the carbon to cool down and did not cool the piece in water.

Spinner bead

Again, the fire scale was gone.

Feb 12 2010

More Options for Firing Copper

So far a few options have been suggested for firing Quick-fire copper clay:

1. Torch-firing (for small pieces only);

2. Hot firing – putting the piece in a hot kiln, removing it while hot, and quenching in water;

3. In a fiber blanket box, with a little carbon, for two hours.

The third option is the same as the method mentioned in the Quick-fire bronze schedule, except that it requires two hours instead of just one.

Actually, there is an another possibility, which does not require handling a hot kiln or waiting 2 hours. If you fire copper alone, you can compensate for time with temperature. (This is true for copper, but not for bronze!) I fired copper following the firing schedule for Quick-fire steel clay. I went up to 1800°F/982°C in my top loader kiln (1880°F/1026°C in a front loader kiln), and held for 1:00 hour.

Here are the photos of before and after:


Out of the kiln

Out of the kiln



You can find the instructions for making a spinner bead like this in my book: Silver and Bronze Clay: Movement and Mechanisms, pp. 88-94. In this case, the bead and the spinner are fired at the same time.


Out of the kiln

Out of the kiln



As you can see from the second example, unlike copper and silver, copper and steel will not alloy and melt as a result of spending a long time in contact under high temperature.

Without steel present in the box, it does not seem necessary to fire at such a high temperature. So my fourth suggestion is:

4. Place in a fiber blanket box with a little carbon on the bottom and on top, with no lid.

Fire at 1690°F/920°C in a top loader; 1770°F/965°C in a front loader.
Hold for 1:00 hour.

Of course, the larger the pieces, the more carbon and time are required.

Feb 12 2010

Workshop in The Netherlands

A workshop in The Netherlands has been added to my schedule this year. The dates are: September 27-28, 2010. Please contact:

Otteline Tuitel
Non!Soesa Creatief
Hoogstraat 36A
5271 KJ Sint-Michielsgestel
(South part of The Netherlands, nearby ‘s-Hertogenbosch)

website: www.nonsoesa.nl/hadar_jacobson.htm
email: info@nonsoesa.nl
Phone: +31735516676

Feb 7 2010

Instruction Manuals Updated

Following the discoveries that were discussed in the last posting regarding the firing method, the instruction manuals for Quick-fire Copper, Bronze, and Steel have now been updated. They can be downloaded from the right-hand pane of this blog. The date on the top of the front page of each document is 2/6/10.

I tested this firing method with steel clay (not stainless). I fired in a fiber blanket box at 1800°F/982°C in my top loader kiln (1880°F/1026°C in a front loader kiln). The total firing time was 2 hours.

Pieces shrank some more (about 20%) and were easier to clean up. The surface was textured with a subtle texture of fine sandpaper. With some buffing with a coarse mini-fiber wheel they became shiny. I liked them as they were, so I did not follow up with sanding. That was the easiest finishing job I ever did.

t-Foldi earings 1

So, I may bring some steel clay to my next travel-teaching workshops. It seems that we may have time to play with it.

Feb 6 2010

How to Make a User-friendly Firing Box

As I promised, here are the instructions for making the firing box.

When handling the fiber blanket it is recommended to wear a protective mask and gloves. An alternative to the fiber blanket will be discussed below.

Cut a square out of the fiber blanket, 2 inches longer than your kiln shelf on every side.


Cut off a 2″ square at each of the four corners of the blanket.


Fold the flaps upward and pinch the sides together.


At first the walls may not stay upright. When placing the box in the kiln, support each side with a post. With every firing the box will become more and more stable, and eventually you won’t need the posts.

Alternatively, as Mary Ellin D’Agostino suggested, you can stitch the sides with high-temp wire.


It is important that the walls of the box are a little away from the walls of the kiln chamber.

This box leaves the kiln perfectly clean. It can be used many times. I haven’t replaced mine yet.

In the past I have tried ceramic boxes. I used bisques and they broke after one firing. However, this ceramic box will not break.

t-Fiber alternative

All it is is a ceramic kiln shelf with posts arranged around it. The carbon stays contained in the box and does not spread in the kiln. You can add more posts to build a deeper box.

Feb 6 2010

Make Your Own Shibuichi Clay


Shibuichi is an ancient Japanese alloy of copper and silver, with the percentage of silver ranging between 5% – 25%. There is a very informative article about this alloy in March 2010 issue of Art Jewelry Magazine by Lee Rumsey Haga, which I highly recommend.

I have been often asked about combining different metal clays together, so I decided to try. I made “Shibuichi clay” of 5% silver and 95% copper, using mixed Quick-fire copper and PMC Plus.

One way to measure is to use a scale. To make 10 grams of this type of Shibuichi clay, mix 0.5 grams silver clay with 9.5 grams copper clay.


If you don’t have a scale, roll the clays into layers of equal thickness. For example, roll each clay between two stacks of 4 cards.

Next, use a straw or a another cutter to cut one circle of silver and twenty circles of copper out of the layers.


To make an alloy with 15% silver, cut 3 circles of silver and 17 circles of copper.

To make an alloy with 25% silver, cut one circle of silver and 3 circles of copper (use a bigger cutter, of course).

Then mix the clay with your fingers, and roll it under the rolling pin over an over until you get a homogeneous color.

I pressed the clay against a texture with high relief.


I fired it with a torch for 6 minutes from the moment the binder had burnt off, and immediately dipped in water.


I found that torch-fired Shibuichi clay is stronger than torched-fired copper clay.

I also tried it in a kiln. Using my new firing method as described in my previous posting, I fired it for 1:00 hour at 1470°F (800°C) in my top loader kiln. In a front loader, fire at 1550°/843°C.

At this point, you can either start playing with patinas or, if you want to clean the piece first, dry it thoroughly on a warming surface.

Shibuichi is very receptive to patinas. Here are some examples:










Heat patina

Heat patina

The last example was done by gently heating with a torch and dipping in water when the desired color was achieved.

Since metal clay is so porous, you will need to apply the patina more than once. I placed the piece on my warming surface and applied it with a brush. At first the liquid was totally absorbed into the metal. With every further application the colors developed more and more. Sometimes they developed after I removed the piece from the warming surface and let it cool down.

When the color was achieved and the piece was dry, I sanded the high part of the relief, first with 220-grit sandpaper, then with 400 grit.

The patina can be sealed with lacquer spray or with sealers from the sources below.


Rust, blue and green patinas are available from hardware stores, or from craft stores such as Blick and Michael’s. The series is called Sophisticated Finishes.

t-Rust patina

Another source is www.sculptnouveaux.com. They also have different sealers and their products come with full instructions.

Feb 3 2010

New Firing Method – Continued

My new firing method seems to be improving as I continue to test it. Here are a few results from further testing, including thick pieces of copper that fired successfully.

Just to clarify, all testing has been done with Quick-fire clay.

The most important thing is: do not cover the carbon with the blanket! If you do, you’ll have to take the pieces out of the kiln while still hot and cool them in water to prevent oxidation. If you prefer to wait until the kiln is cool (as in overnight firing), don’t use the blanket or any other lid.

Here is an updated description of the process. This description replaces my previous posting. Eventually I will incorporate it in the instructon manuals.

1. Fold a fiber blanket into a “box” (detailed instructions in a future posting). The walls of the box should be away from the walls of the kiln chamber. If the walls refuse to stand upright, support them on the sides with posts.


2. Line the inside of the blanket “box” with a ½” layer of carbon.
Arrange your pieces on the carbon bed. As usual, avoid the center. Cover the pieces with another ½” layer of carbon.


Firing Schedule for bronze (even with very thick pieces), mixed pieces, and average sized pieces of copper

You can start the firing in either a cold or a hot kiln.

Top loader brick kiln: ramp at full speed to 1450°F/788°C
Front loader muffle kiln: ramp at full speed to 1530°F/832°C

(You may find that this temperature is too high for bronze. If it is, flat bronze pieces will warp somewhat. You can either hammer them down after firing or lower the temperature.)

Hold for 1:00 hour.

You can take the pieces out of the kiln while still hot or wait until they cool down. Overnight firing works fine. If you take them out hot, use heat-protective gloves.

After firing, most of the carbon will have turned into ash. Pick up the fiber “box” from both ends and lift it out of the kiln. All the ash stays contained in the box; not a grain of it is left in the kiln.


To retrieve your pieces you can pour the ash through a sieve while still hot, into a metal container. Discard the ash.

Here is how the pieces look when removed from the cool kiln:


The black color is not fire scale. Here is how they look after light buffing or sanding:


The pieces shown include bronze, 16 cards (2 craft sticks) thick; bronze, 6 cards thick; copper, 4 cards thick; and mixed, 6 cards thick. All are unbreakable.

Firing schedule for thick pieces of copper (works foo bronze as well)

If you fire only copper, you can always use the “Hot Firing” method:

No carbon is used. Ramp at full speed to 1690°F/920°C (top loader) or 1770°F/965°C (front loader). Hold for 30 minutes. Remove from the kiln while hot, and cool in water.


Instead of a ½” layer of carbon, cover the pieces with a 1” layer.

Top loader brick kiln: ramp at full speed to 1470°F/800°C
Front loader muffle kiln: ramp at full speed to 1550°F/843°C

Hold for 2:00 hours.

Important note: think of the pieces in the carbon in terms of food in the microwave. There is a fixed amount of energy divided among the pieces. The more pieces there are, or the bigger they are, the less energy each of them gets.

Therefore, there is no point in pushing the envelope. Since the firing is now so much shorter, if you are in a hurry (as in a classroom situation), you can fire a few pieces at a time, one firing after another, without cooling the kiln. (Not having to wait for the kiln to cool reduces the overall firing time even more.)

When firing bronze, increasing the amount of energy by increasing the temperature is not an option since the bronze will blister. When firing just copper, thin or thick, small or large, raising the temperature is an option, and it’s still being tested.

Firing Thick or Large Pieces

Again, the “Hot Firing” schedule can be used.


Cover the pieces with more carbon, as much as the box allows. Again, do not use a lid.

Ramp at full speed to
1000°F/538°C (top loader) or 1100°F/593°C (front loader)
Hold for 30 minutes to 1:00 hour (depending on the size)
Ramp at full speed to:
1470°F/800°C (top loader)
1550°/843°C (front loader)

Hold for 3:00 hours. (Time may be shorter, still testing.)

In this case, not all the carbon will have turned into ash and you may want to reuse what is left after vaccuuming.

Feb 2 2010

Workshop in France and other Scheduling Issues

en français*

The deadline to register for my workshop in France this summer is March 15.

I am aware that the workshop is a long time from now, but because this is such a long trip, a lot of arrangements need to be made ahead of time.

Here is the class information again:

Guilde PMC Francophone, Ploemeur, Morbihan FRANCE
website: www.guildepmc.com

e-mail: Guilde.pates.a.metaux@gmail.com
or contact guild president Angela Crispin,
e-mail: ange.est.la@wanadoo.fr

Also see these links:


On another note, the structure of my workshops for people from out of town has changed:

Groups from out of town or out of state are welcome to schedule an intensive workshop at my studio. The workshops will take place on either Friday, Saturday and Sunday, or on Monday, Tuesday and Wednesday. The hours are 10am – 3pm. A minimum of 4 people is required. If you would like to schedule a workshop as a group please contact me for dates and costs. Please see details here.

*La date-limite à s’inscrire à mon atelier en France cet été est le 15 mars.


Guilde PMC francophone, Ploemeur, Morbihan FRANCE
site Web : www.guildepmc.com

email : Guilde.pates.a.metaux@gmail.com

ou Angela Crispin
email : ange.est.la@wanadoo.fr