From grey
to metal
What you are holding is not clay. It is powdered metal waiting for fire.
This is not modelling clay
Metal clay was developed in 1990 in Japan, at Mitsubishi Materials, by the metallurgist Masaki Morikawa. The idea: to make malleable a metal that is not.
What you knead is a mixture of three things. Microscopic metal particles, fine silver or bronze. An organic binder, a plant-based glue that holds the grains together. And water, which makes the whole thing supple.
The metal is already there, all of it, from the very first gesture. The rest is only temporary scaffolding.
The same material, three times
Paste
Soft, damp, forgiving. You shape, you crush, you start again. As long as there is water left, nothing is decided.
Dry greenware
The water has evaporated. The piece is hard but as fragile as a biscuit. This is the moment to file, drill and sand. One fall breaks it.
Metal
The fire has burned off the binder and welded the grains. Only the metal is left. Nothing more can be added without a tool.
Sintering
Under the flame, two things happen one after the other.
First the binder burns. It catches fire, smokes a little, disappears. That is normal and it is spectacular: do not back away.
Then the grains weld together. That is sintering. Heated long enough, the metal grains fuse at their points of contact — without ever melting. The metal stays solid from start to finish. It simply compacts.
And that is where the shrinkage comes from. The binder took up space; on leaving, it leaves a void that the grains fill by moving closer. Your piece shrinks by exactly what the glue occupied.
Fine silver 999
The easier of the two. It forgives, it does not oxidise, and it needs no product afterwards.
Bronze
More demanding. The copper it contains oxidises in air, which changes both the timing and the finishing.
In a workshop, bronze is normally fired in a kiln at 820 °C for 30 to 60 minutes, buried in activated carbon to deprive it of oxygen. With a torch you work in open air: faster and without a kiln, but pieces must stay small and pickling is needed after firing.
The five stages
01 — Knead
Take out only what you need and close the bag immediately: metal clay skins over in the air within minutes. Work on a lightly oiled surface so it does not stick, and keep your fingers damp.
02 — Shape
Shape one size above your target size: the shrinkage will take care of it. The mandrel serves as both template and reference.
As long as the piece is damp, everything is reversible. You can knead it back as many times as you like.
03 — Dry
This is the step people skip and regret. A piece that is still damp bursts under the flame: the water turns to steam all at once and blows the material apart.
The mirror test: rest the piece for a few seconds on a cold, smooth surface. If a halo of condensation appears around it, there is water left. Wait.
Do not force-dry a large piece: thermal shock cracks it.
04 — Fire
On the firing brick, flame about two centimetres away, in small continuous circles. Never hold it on one spot.
The binder catches fire first — let it finish. Then the colour rises. As soon as it is there, start timing: it is the time at colour that welds the grains, not the total time under the flame.
05 — Finish
Quench in water or cool in air. Never quench a piece set with a stone: the thermal shock shatters it.
The metal comes out white and matt. The brush turns it satin, then bright if you keep going.
Four rules, non-negotiable
Age. Kit not recommended for anyone under 18. It is not a toy.
Space. Non-flammable surface, never wood or plastic. Ventilated room: the binder burning off gives off smoke.
Body. Heat-resistant gloves — never nitrile or latex, which melt onto the skin. Metal tongs for every move. Glasses, hair tied back, closed shoes.
Time. Ten minutes before touching the piece bare-handed, thirty for the brick. Metal stops glowing long before it can be handled.
When it goes wrong
My piece swelled or blistered.
There was water left. The steam tried to escape and lifted the material. Either the drying was insufficient, or it was so brutal that it formed a sealed crust on the surface.
It crumbles or breaks on its own.
Incomplete sintering: the grains did not weld. You did not hold the colour long enough, or you started timing from when you lit the torch rather than from the colour.
It can be saved: fire the piece again, respecting the time.
It melted or slumped.
Too hot. Just before melting, the surface turns bright and liquid, like a trembling mirror. The moment you see that, pull the flame away.
A melted piece is lost as a piece, but the metal itself is not.
My bronze is completely black.
That is copper oxide, and it is normal: you fired in open air. It takes pickling to remove; the brush alone will not do it.
My stone shattered or changed colour.
Only synthetic stones — cubic zirconia above all — survive being fired in place. Natural stones contain fractures and inclusions that burst in the heat, and many discolour.
Always check that a stone is rated for firing in place before setting it before firing.
The kit contains all of it.
The clay, the torch, the firing brick, the mandrel, the brush and the guide.