Sunday, March 23, 2014

What is Metal Clay



What is Metal Clay
(a non-technical introduction to the medium)
by Laura Bracken

 Here are the basic steps involved when I create a piece of jewelry from metal clay.

First I’d like you to know that “metal clay” is solid metal that has been powderized.  Added to that are small particles of an organic binder so that when mixed with water, a clay-like substance is formed.  There is no “clay” in metal clay.  Metal clay is pure metal and an organic binder.  During the firing process, the organic binder burns off and you are left with only pure metal again.  So here’s how it works.

Metal clay is a form of powder metallurgy.  This is what the powderized metal and organic binder look like before you add water to it (this happens to be powderized Bronze, which is an alloy of copper and tin).

You add water and mix it up to a clay-like consistency.

Then you use this clay-like substance to form your piece.  You can roll the clay into flat sheets, roll it into balls, press textures into it, sculpt, build, carve, etc.

You can mix certain metals in certain ways for really cool effects.  The main metals I work with are Bronze, Copper, Steel, a lighter colored Steel Alloy, and very rarely Silver.

You can also embed certain stones into your designs so long as you check first to be sure they’ll survive the firing temperature.  Most of the stones I use are natural Rubies and Cubic Zirconia.
 
 
 
When you have your pieces the way you want them, you let them dry.  Here are five pieces that are dried but not yet fired.  The metals on each piece are Bronze, Steel, and Copper.
 
Then you place the piece in a bowl filled with carbon (made from coconut shell or husk) and fire it in a kiln.  The firing temperature ranges from about 1400-1850 degrees Fahrenheit and it takes about 3 hours for one firing in the kiln.  Some of the metals require two separate phases of firing, with a cooling down period in between.  Metal clay is not an instant process.
  
During the firing of the piece of metal clay, two things must happen.  First, the organic binder must thoroughly burn out.  After that, the remaining metal must sinter.  Sintering is where powderized metal is heated to a temperature below its melting point.  Then the particles of metal begin to fuse together into one solid piece.  A finished piece of metal clay jewelry is more porous than jewelry made from sheet metal, but it is still strong, solid metal.

Once your pieces are out of the kiln, if no repairs are necessary (repairs can be made with fresh clay and re-firing) it is time to clean the metal.

Sometimes the metal pieces get a really neat color patina from the firing.  These vibrant colors usually fade with time.
 
For textured pieces of metal, I clean my piece with a radial disk tool on my dremel.  
If the piece needs a smoother finish, I sand aggressively with increasingly finer grits of sandpaper, usually starting out at 120 and working my way up to 1000.   
 
I created a cheap contraption to keep the ensuing metal dust contained.  Two holes cut into a lidless box with cut-off kitchen gloves taped into the holes.  Two lengths of Saran/plastic wrap across the top of the box, overlapping so they touch but you can separate them to slip things (like your dremel) into the compartment.
 
After the piece has been sanded and polished, I can give it a patina with liver of sulfur if I want to emphasize any color contrast.  This works well between copper and bronze as the copper darkens and the bronze stays bright.  This is a speeded up process of the natural oxidation that would occur if we just left the piece alone, exposed to the air, for months and/or years.
 
  
 
 
 

The final step, adding a sealant, is optional and there can be different reasons to choose this.  These reasons include:

  • If I want the piece to be preserved with the colors it has at that moment.
  • If the customer reacts to copper and wants a barrier between the copper and their skin.
  • If the piece is steel, I often add protection since the iron in steel can cause rust when it gets wet.

I hope this explanation helps anyone who wanted to become more familiar with the process of metal clay.

I am accredited to teach both Hadar’s Clays and PMC.  


2 comments:

  1. Thanks, Laura. This was written very clearly. I may be inching nearer to dabbling again. ;) Can you tell me what determines the temperature within the range you mentioned? Is it size? P.S, this is Annie from LE. :)

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  2. Hi Annie! Thank you for the nice words about my article. As far as determining temperature, I first go by what the instruction manual says. From there, I usually run some tests (since all kilns are different) to determine the best temp for that clay in *my* kiln. There are a few other factors that may make you want to increase or decrease the temp a bit (crowding, size, combinations, etc)... but I handle those on a case by case basis. Please share with me when you start working with metal clay. I'd love to see what you make.

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