Sunday, September 05, 2010
The Joy of Metal Clay: Copper Clay Part 1: Art Clay Copper
Last week, I talked about many of the current base (non precious) metal clays available. For the next few weeks I hope to cover some of these types of clays more in depth.
Today, I am going to start with Art Clay Copper.
Art Clay Copper like other metal clays is made up of microscopic particles of metal (in this case copper) mixed with water and a binder. Once fired pieces made with Art Clay Copper end up being pure 100% copper.
First let me start by saying that Art ClayCopper is somewhat unique compared to most of the other base metal clays as it does not require to be covered with firing with carbon which makes it appealing to those who wish to stay away from carbon (messy and not a good idea to breath in) or those of you who want to torch fire or use your Speedfire Cone system.
The tools that one uses to create pieces with Art Clay Copper are the same as the ones you would use with any other metal clay. Wash your tools between use between different clays to preserve the purity of you metals and any problems with firing.
One important difference I have noticed with Art Clay Copper is that too much oil mixed into the clay can create a crumbly and difficult to work texture. Now don't panic. What I have found is that you can still you olive oil on your hands and textures but you don't want the oil to be pooling in the texture sheets or to find that when roll out the clay you get a film of oil over the clay. I have found that adding a drop or two of oil to your texture sheet then rubbing it in with a toothbrush to spread hte oil works fine. If you have too much oil use a paper towel to remove the excess. Bottom line, if you find that your clay begins to be crumbly and will not form a ball even with efforts to rehydrate it too much oil may be your problem.
The other important tip that I have found is that the clay needs to be conditioned when it is removed from the package. Often I have found that the clay is tough to work with straight out of the package. Kneading the clay and adding moisture for a few minutes will improve the clay significantly. There are different techniques to achieve this, my method includes rolling the clay painting on a layer of water and then folding the water in and then rolling and repeating. I will often repeat this technique at anytime the clay gets dry or difficult to work. (You can refer to my post cracking clay on how to rehydrate silver clay for some photos of this technique, Sometimes I will recommend to do this between two sheets of plastic helps contain messes for beginner, I find that over time you will learn to handle your clay more easily and neatly)
The final tip is to make sure that you attach your pieces well when you attaching two pieces of Art Clay Copper. I have found that my students have a harder time making a good attachment with Art Clay Copper. As for suggestions, I have two thoughts: first, make sure you use fresh paste (you need to make your own paste with Art Clay Copper and the paste can oxidize over time, noted by it turning darker, this paste will not attach as well as fresh and shouldn't be used) and second, hold your pieces together for 20 seconds to enhance the sticking.
Drying Art Clay Copper is similar to silver metal clay. Some people will use a form of heat to dry their clay (such as a dehydrator or an mug warmer). The key as with any metal clay is to make sure you don't heat the piece so hot that you burn off the binder. My general rule of thumb is to keep the piece no hotter than 200F but the literature for Art Clay Copper states that it is at 480F where the binder will be destroyed.
Once your piece is dried you will can fire the piece.
The general guidelines are: "fire a piece no large that a US Silver dollar and 35 grams on a firing brick and heat until cherry red for at least 3-5 minutes, depending on size. Pieces 10 g and 1mm or less in thickness can fire for 3 minutes: pieces up to 25 g and 2.5 mm thick can fire for 5 minutes."Art Clay World - Art Clay Copper Booklet
I have two comments on these guidelines.
First, is that I think that anything over 15 grams will likely be a challenge to keep hot enough with a simple butane torch. The sintering temperature for Art Clay Copper needs to be around 1778F which is much hotter that traditional silver clay. I have found that at times it is hard to maintain the heat with a handheld butane torch. (of course there are other torches you can use but this is what I have found with the common butane torch)
Second, l recommend torch firing any piece for at least five minutes! It is important to make sure that you start timing only once the piece start glowing red and that you need to keep it glowing bright red for the full five minutes. I experimented once while firing my Art Clay Copper where I allowed it to drift away from this bright red colour briefly during the period of five minutes (what I mean is that its colour became a lighter rosy colour indicating that the temperature has reduced slightly - below ideal sintering temperature). I decided to see what would happen so I quenched the piece and then began to brush it with a steel brush. I noticed the texture didn't seem quite right so I tested it by banging it with my hammer. The piece broke indicating it was not sintered properly. This is a big problem with torch firing, under firing, so be aware.
Once you have fired your pieces you need to quench them. Quenching is important as it will reduce the amount of oxidization on the piece.The longer the copper is exposed to high heat and oxygen the thicker the layer of oxidization over the piece.
Here is a picture of the bits from oxidization that have fallen off in the bottom of my quenching bowl.
I have found that kiln fired pieces will develop more of a coating on them as they are exposed to heat and oxygen longer. I have also noticed that due to the coating that you loose you will loose some thickness in your pieces. Art Clay Copper will shrink approximately 10 percent. I have found that you will loose some thickness in any copper wire that you embed fire due to oxidization.
Below is a picture a fired piece (on left, note the burgundy oxidized layer) and a dry unfired piece on the right):
The General rules for kiln firing are: "Pre-ramp the kiln to 1778F. Place the piece into a preheated kiln at 1778F and hold for 30 minutes. Remove the red hot piece with tongs or tweezers immediately after firing is compete and quench with cool water so that most of the oxidized layer peels off to reveal perfect copper. You may also put the piece into a room temperature kiln and ramp up at maximum speed to the listed temperature, but pre-heating the kiln is recommended."
I have a couple of thoughts here. One is to be sure you use proper safety equipment when doing this (kiln goggles, heat resistant gloves, tongs and other) Another important thing to note is that I have found there are times that my pieces will stick to the kiln shelf at high temperature (they will come off when cooled). In order to prevent them from sticking you can use kiln paper on your shelf under your piece. Other recommendations I have heard it that you will get less oxidization on the piece that is next to the shelf so put your "good side" down. One other thing, if you choose to proceed make sure your kiln is on a fire proof table and that you have a large pot to put your pieces in to quench (Be really careful you don't want to drop these 1778F fireballs on the ground or your BODY!!! - I work in a room with a concrete floor and a large metal bucket full of water that I slide the pieces into )
PICKLING & POLISHING:
Once the pieces are fired they will often require pickling. Pickling is used to remove any remaining bits of oxidization. I found that I need to use Sparex to pickle my pieces and was not able to use any less toxic solutions.Put your pickle into a container that you will not use for food. Make sure you do not put any steel into the pickle. I have copper tongs but find it easier to attach my pieces to a copper wire (as I find it hard to fish out my pieces from the bottom of my pickle pots.) Be sure to use safety procedures when working with your pickle!!!!
Once you have removed your oxidized layer you can brush your piece and then polish and/or tumble.
This clay was first released to the public in December 2009. I believe we will see it grow and change over next few years. One area that I hope to see improved is the ability to make repairs on fired pieces. I have yet to figure that one out.
Art Clay Copper can be a fun medium to work with and with it about a fith of the cost of silver clay it more economical too!!!. Enjoy.
There are detailed directions on Art Clay Copper at the Art Clay World website in the Art Clay Copper Booklet.