DIY Bronze Clay - Filigree Egg

This my second Instructable on DIY metal clay, this time using atomized bronze powder to make bronze metal clay (base metal clay).    See DIY Copper Clay Trilobites for a brief history of precious metal clays and base metal clays.

Metal clay allows anyone to make complex objects from metal without traditional metal working skills - no soldering, forging, casting etc.  Shape metal clay, dry it and 'fire it' to produce a sintered metal object.  Sintered metal consist of tiny metal particles that are fused together, but not melted into solid metal.  Sintering allows the metal clay to retain its shape, whereas cast metal must be melted and poured into a mold to form a shape: a long process.  Metal clay is heated close to the melting point of it's metal, and the metal particles partially fuse together to form a metal matrix with tiny holes, about 70-90% the density of solid cast metal.  Think of a bucket of ice cubes left at room temperature.  After a while you try to pick up an icecube and you end up with a hunk of icecubes stuck together along the edges.   

You can buy commercial metal clays made from pure powdered silver, and more recently base metal clays are available - copper, bronze etc.  Commercial metal clays are high quality, somewhat expensive and must usually be mail ordered.  They also come only in selected package sizes... what if you want to only use a little clay, or you want LOTS all at once?  A work around is to make your own metal clay.  Just a word about expectations:  DIY metal clay will probably not produce quite the excellent quality of commercial metal clay - but I've had very good results and a lot of fun making my own stuff.  This is my experience trying to make something for the EGGBOT contest.

Step 1 Bronze clay recipe

Metal clay consists of organic binders, water and atomized metal (-325 mesh or smaller), sometimes with a few added conditioners for better handling, flexibility etc. Here is a bronze clay recipe, it's very similar to my previous copper clay recipe, but with one different binder.  You can vary organic binders and see which ones you like best.  Just use binders that are non-toxic and burn cleanly.  Nasty binder residue can interfere with the sintering process and you could end up with a fragile hunk of charred, black metal, not the wonderful sculpture or jewelry you envisioned.  (I even tried using egg white and egg yolk as a binder, but neither worked well... too bad, there went my easy 'egg connection').

  ALWAYS wear a fine particulate mask when handling dry powders, preferable N95 - no excuse not to BE SAFE and use safety equipment.

Bronze Clay
1/2 tsp. potato starch
1/4 tsp. powdered xanthan gum (do not breathe in the powder! It forms a VERY gummy slime when mixed with water - horrible for your lungs) 
3+ Tbsp atomized bronze*
distilled water in a small spray bottle.
other options -  a few drops of glycerin, oil or a drop of dish soap can change consitency.


Wear your mask and carefully mix dry ingredients until you have a uniform mix, no visible clumps of startch..
Spray surface with some distilled water and carefully stir. Add more spritzes of water and keep stirring until the mix starts to clump together. Mix well between  spritzes until your mixture starts to feel clay-like. Lightly oil your hands with olive oil or natural hand balm and squeeze mixture. If it holds together then you can knead by  hand. If mixture starts to crumble, work in a little more water. If it is very sticky, let it dry a bit and rework, or add a little more metal powder or cornstarch.

You can let clay rest in a sealed plastic bag or container.

You can also mix some of the clay into a smooth paste, like peanut butter, which can be extruded in a clay press, or icing bag.

* Use metal at least -325 mesh, about 44 micron particle size.  -325 mesh atomized metal is sold for use in 'cold casting metal', basically a cast  resin binder and metal powder to achieve a look similar to cast metal.  Various art suppliers sell -325 mesh atomized metal, also available online at Doughlass and Sturgess. Tap plastics  sell powdered bronze in their retails stores, it's a copper/tin alloy.  Sometimes bronze powders contain other metals too, such as copper/tin/silicon.  Each alloy has a slightly different melting temperature.