1 Sep 2008
   
PRECIOUS METAL CLAY (PMC), ART CLAY SILVER, AND OTHER METALS
Firing times will depend on the wattage of your microwave oven.
Regarding the "Art Clay Silver" document: PLEASE NOTE UNDER #3 WHERE IT SAYS, "HEATING TIME WOULD TAKE LONGER IF THE WATTAGE OF THE MICROWAVE IS LESS THAN 500 WATTS...." This also means that if your microwave's wattage is more than 500 watts that your beginning firing times should be less than the times shown in the chart below.
I am awaiting more information about using how to use copper in the microwave kiln.
The inside of the microwave kiln reaches very high temperatures up to 1652 F. Notice the melting point of these metals: (Glass melts around 1425 F).
| Copper |
1357 F. You can experiment with what you can do with fusible copper sheets such as sandwich between pieces of glass. This could make a mess and ruin your kiln in a hurry! |
| Brass |
1652 F. I sandwiched a brass letter between layers of glass just to find out what would happen. |
| Silver (not PMC)** |
1763.2 F. Because of this, one source recommended refiring silver clay no more than a second time at 3 minutes. |
| Gold |
1947.52 F. Do not fire gold metal clay in your microwave kiln. But I have successfully used a Ferro Gold Rush Ceramic Pen. |
THE FOLLOWING INSTRUCTIONS ARE FOR SILVER CLAY:
Prefiring test: To avoid melting from over firing, do a test firing with 1 gram of flattened, DRIED clay. Draw a line around the outside of your unfired piece, then fire. If the contraction is 8 to 10%, you successfully fired the piece. If art clay melts, shorten the time. If it crumbles, add more time. PMC will shrink about 10%. If you drop it from a height of about 2" above a table and you hear a metal sound, it has been successfully fired. If not, fire again with less time.
If you have never worked with precious metal clay or silver clay, PMC3 might be your best choice. PMC3 has minimal shrinkage and fires at a very low temperature which is very good for your kiln. You can also use certain stones and enamels with PMC3. PMC+ requires a much higher firing temperature and longer firing times. NOTE: I do not recommend putting stones in a microwave kiln as I have never tested them.
PMC3 is best suited for glass applications due to its lower firing temperatures. It is recommended for rings, charms, and pendants. It fires in 10 minutes at 1290 F or 30 minutes at 1110 F** in a traditional kiln. I decided to work with PMC3 because of the lower firing temperatures, which means shorter firing times. The firing process leaves a metal that is less dense than conventional sheet or wire. This means that a piece of jewelry made of PMC is lighter than the same piece made via traditional fabrication; therefore, PMC is not recommended for applications such as findings.
I personally have not yet tested Art Clay Silver to determine what the differences are, if any. Using microwave kilns require EXPERIMENTING!!! But I would recommend that you use whatever formula requires the lowest firing temperature.
Fashion your piece using your fingers and tools, let the project thoroughly dry, fire your piece, and finish by sanding and polishing. (Your piece must be completely dry or it will be deformed. It will also damage your microwave kiln!)
When firing a 3 dimensional piece, support it with a soft ceramic fiber blanket to prevent collapsing under its own weight.
What is the clay volume limit for firing a 3 dimensional piece? Less than 30 grams (which is 1.05 oz). Microwave kilns are not recommended for hollow pieces.
Size Limitation: Small microwave kiln: less than 4 cm (1 1/2""). Do not fire anything larger than this or it will melt.
The size/weight of your project has everything to do with the firing times. Most instructions say to watch for the orange light to appear, turn the microwave off and immediately refire to desired firing time (Use the table below).
Approximate firing time for Art Clay Silver in small microwave kiln:*****
3 grams (which is .1058 oz) 1 to 1.5 minutes
3 -10 grams (which is .1058 oz - .3527 oz.) 1.5 - 2 minutes
10 to 30 grams (which is .3527 oz - 1.0582 oz) 1.5 - 2.5 minutes
rope shape or thin piece 1 min to 1.5 min.
| 1. |
With a pencil and paper, draw an outline of the outside perimeter of your dried clay piece. |
| 2. |
Place a piece of shelf paper on the microwave kiln base. |
| 3. |
Place your project on the shelf paper. |
| 4. |
Place microwave kiln into microwave oven. Heat until it becomes orange. you can see the inside through the hole in the lid. Turn off. |
| 5. |
*****SEE NOTE ABOVE ABOUT FIRING TIMES! I RECOMMEND YOU START TESTING AT ONE MINUTE. Heating time: Approximately 3 minutes until the color changes. If the hole on the top does not change to an orange color, add extra one minute by setting the microwave timer. You may repeatedly add extra one minute until the hole on the lid becomes orange. TURN OFF |
| 6. |
NOW RESET FIRING TIME : This depends on weight of your project! (See chart in previous paragraph). Firing for more than the chart shows, you risk melting your project. Pre-firing a test piece is recommended! |
| 7. |
After firing, take out from microwave oven at once, using gloves. It usually takes from 20 to 30 minutes to cool down. Do not open the kiln while it is still hot. Use tweezers to pick up the fired piece and then: |
| 8. |
Check the size of the fired piece against your drawing in #1. If the contraction of the fired piece is less than 8 to 10%, it is not successfully fired. You need to follow steps from 2 to 6 again to complete firing. Art clay silver contracts from 8 to 10% when fired. It is important to do this step for checking if your piece is successfully fired. |
You will notice that the surface of the fired piece is white. This is due to a crystallization of the silver powder. I remove the powder with a small brass brush.
Silver cleaning solution: sterling silver contains copper and when it gets into high temperatures, it develops a black covering, called fire-scale. To remove it you can mix 1/2 cup warm white vinegar and a tablespoon of salt and soak the piece in it for 20-30 minutes. Note: do not use the stainless steel tweezers with this solution.
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