Friday, December 7, 2012

Problem with Embedding Sterling Silver Wire

by Janet Alexander
Technical Advisor

I had a student email me about a problem she had with some embedded sterling silver wire in her piece. She decided to use the sterling silver because it is stronger and holds its shape better than fine silver. She embedded the sliver between two layers of PMC3 metal clay making it a loop coming out of the bottom of the piece. It was to hold a dangling object.

She said she fired the piece at 1300 F for 30 min in order to give it the best strength and highest shrinkage. She chose not to fire it at 1650 F because sterling silver is an alloy of copper and silver, and copper has a lower melting point than pure silver. Her problem is that the sterling silver wire became weaker and broke easily.

I responded with this answer:

Firing sterling silver above 1200 degrees F makes the metal brittle and can actually cause it to crumble. The melting point for sterling silver is 1640 F / 893C. Maybe using a fine silver embedded jump ring or incorporating a hidden bail made from PMC3 clay would have worked better. This way, the piece could be fired at 1650 F for two hours.

Keep the questions coming! I hope to hear from you all soon! In the meantime have fun claying around.


Terezi said...

Yeah, my understanding is that the ENTIRE surface of the sterling must be coated with metal clay, OR at least be depleted, or it won't make it thru the firing. In fact, in the class I took several years ago, we did both (depletion fired the sterling, then coated it with PMC paste). This was for a cuff bracelet with added dimensional metal clay elements.

Sue McNenly said...

This isn't making sense to me? I embed sterling wire in my sterling clay, fire it in the 2 phases (air/carbon) and I've had no trouble? I've done this a number of times, and I like to test my pieces for durability, always with success. Any thoughts? Is this a fluke for me?


Janet Alexander said...

Hi Sue,

The difference is that you used both sterling sliver wire and sterling silver clay. The problem I responded to is she used PMC3 (fine silver) with sterling silver firing it in a kiln without carbon. What happens is the sterling silver metal tarnishes and won't stick to the fine silver when used in this manner. By raising the fine silver to the outer layer of the metal keeps the sterling silver from tarnishing.
When we fire the sterling silver clay in carbon it creates an oxygen deprived atmosphere keeping the sterling silver from tarnishing.
I hope this helps.


Janet Alexander said...

It is not necessary to coat the entire surface of the depleted sterling silver with paste. I do use a mixture of oil paste (PMC3 slip + lavender oil) to the area I am adhering to the piece.


wormgirl1 said...

Have fired sterling silver open shelf *many* times at 1650F and yes, wire does become brittle and yes it does tarnish, but incredible that no one has ever heard of annealing...? Pieces have to be annealed post firing to “soften” them, and then work hardened to suite. Ganoskin has excellent information on the annealing process. Oxidation is easily solved with a solution of ammonia and mild detergent while tumbling. My experience. Your mileage may vary.