WHEN Australian silversmith Ian Ferguson first tried his hand at an old
Japanese metal-working craft, he realised that it wasn鈥檛 going to be easy. Try
as he might to forge a neatly layered block of silver and copper, all too often
he ended up with a puddle of molten metal trickling off the anvil.
Overenthusiastic hammer blows sent metal sheets flying in all directions. And in
one unfortunate experiment, when he flattened a block of white-hot metal, a fine
spray of molten brass peppered holes through his clothes. 鈥淚t felt like being
flayed with a bunch of nettles,鈥� he says.
Not one to give up easily, Ferguson closed his business, sold his house, and
set off for England. With the help of state-of-the-art technology used for metal
bonding research at Oxford University, he has since transformed an arcane craft
into a trusted technique. Now he has started to make masterpieces of fine metal
that would have been beyond the dreams of the original Japanese artists.
The metal-working technique has its roots in ancient Japanese techniques for
decorating the swords of the samurai. Some one hundred years ago, artists began
to diversify, decorating a range of artefacts from opium pipes to vases. Ancient
craftworkers fused layers of different metals together 鈥攖ypically alloys
of copper, silver and gold鈥攖hen carved and hammered them to expose the
different layers and create multicoloured patterns. The swirling patterns often
looked like knotted wood, giving the technique its name, mokumegane: literally,
鈥渆ye of the wood grain metal鈥�.
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To achieve this effect, the handful of traditional craftsworkers who still
use the technique stack thin sheets of metal in layers, tie them together with
metal wire, and heat the sheets in a blacksmith鈥檚 furnace. Although the
temperatures reached are below the melting point of each metal, the heat excites
metal atoms and encourages them to diffuse into neighbouring layers. The metal
atoms mingle across a region only a few micrometres thick and the divide looks
razor-sharp, but the resulting bond is extremely strong鈥攕trong enough that
the melded material can be pressed into a flat sheet without the components
separating.
It鈥檚 this flattening part of the process that gives mokumegane its
characteristic fine swirls and lines. Channels, holes or more intricate patterns
are drilled into the layered block before it is flattened. And as the metals
squeeze like toothpaste out of the layers around holes and channels, they rise
to the surface where they appear as stripes, knots and bullseyes.
Ferguson came across the technique at a workshop in Perth, Australia, in
1986. When he went home to try it out, he had little success. Finding the right
moment to remove the metals from the forge seemed impossible. A moment too early
and the sheets simply slid off each other, a moment too late and they melted
into a blob. 鈥淵ou can be a second out and it鈥檚 a disaster,鈥� he says.
Eventually, he got the hang of it, but the process was still laborious. As
the metals sat in the forge, he had to watch them like a hawk. This was the only
way to spot the slight darkening of the metals as they drew in energy at the
moment they started to flow. Worse still, the rules had to be completely
rewritten with every new combination of metals.
Colourful combinations
Japanese tradition had restricted the Oriental craft to alloys of silver,
gold and copper, which gave knotted patterns in a limited range of white, grey,
red, brown and black. But using different combinations of metals, Ferguson
reckoned that it should be possible to get shades of yellow, green or even the
oily purple of titanium.
That was easier said than done. For instance, Ferguson wanted to fuse nickel
silver, which contains copper, zinc and nickel and another alloy, called Monel,
which is mainly nickel and copper. This would allow him to create swirls of
black and silver鈥攁 colour combination that is impossible using traditional
alloys. But these metals are both extremely stable, and melt at temperatures
above 1100 掳C. Encouraging the two to bond proved so difficult that in the
end Ferguson resorted to brute force. He heated the layers until they were white
hot, then dropped a 90 kilogram weight on them from a height of almost 4
metres.
鈥淭hat got me thinking that there must be a better way,鈥� says Ferguson, who
started to read about modern bonding techniques. He came across diffusion
bonding, which is widely used to make the components of nuclear reactors and
aircraft engines鈥攆or instance, to weld the titanium alloy components that
make the fan blades in Rolls Royce aircraft engines. It needs careful control
not only of temperature but also of the pressure used to squeeze the metal
sheets and of the timing of the process. Unfortunately, Ferguson had no access
to the technology for diffusion bonding in Australia. So it was that year, 1991,
that he decided to up sticks and start a PhD at the Royal College of Art in
London.
At the nearby Imperial College of Science, Technology and Medicine, the doors
of the materials science department were opened to him. Ferguson set up a
makeshift diffusion-bonding apparatus鈥攁 jig to hold the sheets and a
compression ram that could be placed inside a modern furnace. And with two
stainless steel teapots from a local shop, he built a chamber that he could fill
with the inert gas argon. This stopped some of the reactive metals oxidising and
tarnishing in the heat. Later, he enlarged the gas chamber with more help from
the kitchen suppliers鈥攖his time with two asparagus steamers.
Bonding with confidence
For the first time, Ferguson had fairly good control over the process.
Earlier research on diffusion bonding guided his choice of temperature to
between a half and three-quarters of the melting point of the most easily melted
metal. After two years Ferguson had worked up a repertoire of some thirty
combinations that he could bond with confidence. Yet many
combinations鈥攅specially using very reactive metals鈥攔efused to yield
to his efforts. Then in 1993, the materials science department at Oxford
University offered him access to its state-of-the-art equipment. The diffusion
bonder there can fuse layered cubes up to 5 centimetres on a side under tightly
controlled conditions in a vacuum. These blocks roll out into large sheets about
20 by 30 centimetres.
With a grant from the Leverhulme Trust, which funds interdisciplinary
projects, Ferguson started work with Brian Derby, a metallurgist at Oxford.
Derby, who has researched diffusion bonding for several years, was glad of the
chance to work with the art world. 鈥淧eople have always thought of metals as
being a fairly low-tech, smokestack industry,鈥� he says. 鈥淭his was an opportunity
to show that you can do pretty things with metals.鈥�
Their aim was to try out some of the more unusual combinations of metals, and
pinpoint the best conditions for bonding them. Derby was able to shed some light
on some of Ferguson鈥檚 less successful attempts. For instance, although Ferguson
had succeeded in fusing small blocks of copper and Monel at 900 掳C, when he
tried it with larger blocks, the sheets just fell apart. 鈥淚t was horrible,鈥� says
Ferguson, who examined the debris under an electron microscope. 鈥淚t came out all
bubbly and flaky.鈥�
Derby diagnosed Kirkendall porosity, which is caused by differences in the
rates at which two metals diffuse into one another. Copper atoms were migrating
to empty sites in Monel鈥檚 crystal lattice very efficiently, but nickel atoms
from the Monel were more sluggish about moving to the copper side. Because of
this, the copper became weak and full of holes. Ferguson鈥檚 research showed that
he could solve the problem by lowering the temperature to about 600 掳C and
increasing the pressure on the block.
The next challenge was to tackle reactive metals such as titanium. When
titanium reacts with oxygen, it becomes coated in an ultrathin transparent film.
Light reflected from above and beneath the oxide film interferes to give a
spectacular rainbow of colours, just like on a film of oil on still water.
But reactive metals also bring problems. Instead of obligingly diffusing into
another metal, titanium reacts with it and binds into a complicated
鈥渋ntermetallic鈥� compound full of large, elaborate crystals. Metals like copper
deform fairly easily because they have relatively simple crystal structures. But
the large and complex intermetallic crystals are intrinsically brittle. Derby
suspected that rolling layers with intermetallics sandwiched between would make
the material fall apart.
Sure enough, an intermetallic compound showed up under the microscope when
titanium bonded to copper. And as soon as Ferguson started to flatten the
layers, they snapped and cracked into little islands. But to Derby鈥檚 surprise,
the material did not crumble. As the islands formed, the much more pliable
copper flowed into the cracks, holding the sheets together. Ferguson then
oxidised the titanium to give islands of irridescent purples, browns and
electric blues in a sea of copper red. 鈥淵ou get these wonderful patterns,鈥� he
says.
Ferguson says that for forty or so metal combinations, he now has a
dependable recipe. 鈥淚 can guarantee that it will work every time,鈥� he says. He
has already put some of the new metal combinations to use in plates, watch
cases, a decorative egg and several bowls. He has also crafted bowls of copper
and iron, and copper and stainless steel for the Victoria and Albert Museum in
London. Philippa Glanville of the V&A, which is commissioning another bowl
to go on display in November, says Ferguson鈥檚 work is the best example of
mokumegane she has seen. 鈥淣o one has ever applied the process as successfully as
he has,鈥� she says. 鈥淭he colour combinations are wonderful.鈥�
Ferguson鈥檚 work with his new materials has also hinted at all kinds of
curious properties yet to be explored. 鈥淚 made a bowl out of copper and
stainless steel, and it behaves very strangely,鈥� says Ferguson. 鈥淚t seems to
have a memory.鈥� After beating it into a bowl he found that the metal tended to
return to its original shape as soon as it was heated.
Ferguson is aware that few people working in mokumegane approve of liaisons
with the world of high-tech. But he insists that you have to have science to be
a good artist. 鈥淚f you use bad paint and it falls off the canvas, you might
shrug your shoulders and walk away,鈥� he says. 鈥淏ut if your intention was for it
to last a long time, then you鈥檝e failed.鈥�
With help from science, Ferguson and Glanville hope that mokumegane could
flourish in the craft world once again. Ferguson has designed a studio forge
that will allow others to have a go at the craft鈥攂ut without the sweat and
tears. 鈥淚鈥檓 hoping more people will take it up,鈥� he says. 鈥淚鈥檝e got so many
projects in mind that I haven鈥檛 enough time in my life to do them.鈥�