Getting hold of materials that you can trust to be right can sometimes represent something of a problem. It might be that you need to have panels made from a particular material or you are making a triptych and you need to have metal hinges that are made from the same materials that were available 600 years ago
Other pages will tell you about making things but this page is about obtaining the materials in the first place. Here, we'll cover:
- Charcoal Iron; and,
- Quarter Sawn Oak
A bit about the history and why it is difficult to get
When I did metalwork at school, one of the teachers made some wrought iron gates for someone he knew, building them from mild steel bar stock. Online, you can buy wrought iron nails, hinges and all manner of things.
Except that it is not wrought iron.
Wrought iron is a material, not a type of construction.
- Originally, iron was made by mixing charcoal with iron ore and heating it up. The carbon in the charcoal would grab the
oxygen from the iron ore, exiting as a gas and leaving the reduced iron metal behind as a bloom. In addition, the iron ore contains
silica and of course, when the iron forms, it includes chunks of charcoal. The iron never melts in the furnace - if it was allowed
to, the liquid iron would absorb carbon from the charcoal to produce a high carbon pig iron which was not desirable.
When the iron is taken out of the furnace, it is hammered which, apart from making it form a useful iron lump,
makes the larger charcoal lumps fall out. However, it tends to break up the remaining charcoal, leaving smaller bits behind.
Another thing that is in the final iron is the silica from the impurities in the iron ore. This forms sort of glass fibres
that run throughout the iron, making it a composite which turns out to be very strong, malleable and resistant to corrosion.
- The process was then modified so that iron was melted in the furnace and cast to form pig iron which was high in carbon.
Being an alloy - yes, iron and carbon are considered an alloy - it has a lower melting point so it was put into what was
called a puddle furnace where a puddle of molten pig iron was exposed to the air which preferentially oxidised the carbon,
reducing the proportion in the iron and making it solidify. This was then removed and then hammered to form it as before
with the charcoal iron.
This new iron still had the silicates in it making it a composite as before and as before, it was strong
malleable and resistant to corrosion. The difference was that it didn't have the inclusions of charcoal in it.
- The process was modified again, this time, instead of the puddle furnace, you melt your pig iron in a large pot and then
pump oxygen through it to remove the carbon - the Bessemer converter.
Wrought iron was so good a material that there was even a way of converting the steel from a Bessemer converter to a
type of wrought iron developed by James Aston in the USA where iron from the converter was poured into slightly cooler slag
where it mixed and was then worked and rolled so that it had a similar structure to wrought iron.
Nowadays, virtually all so-called wrought iron things are made from mild steel and just given a superficial 'hammered' look so
they are not actually wrought iron.
So, why do we need charcoal iron? Simply, around the time of the renaissance, 600 years ago, iron production hadn't got past the
charcoal process so if a fitting that is needed is going to look the part, it needs to be made out of the correct material. Brass didn't
exist so it had to be charcoal iron.
Getting hold of it
This planet still has one supplier of wrought iron and it is The Real Wrought Iron Company, based at Topp & Co., Tholthorpe, North Yorkshire (UK). They travel around sourcing genuine wrought iron and making sheet, plate and various sections for railings, handrails and so on.
Included is charcoal iron as sheet which is ideal for the my needs. I have several samples of this stuff and it certainly is
different to the stuff passing itself off on the internet as 'wrought iron'. The sizes are all imperial so 3/32" is roughly 2.4mm and 1/16" is roughly 1.6mm.
Quarter Sawn Oak
A bit about the history and why it is difficult to get
Quarter sawn oak panel was the material of choice, six hundred years ago, as it produced a surface that was flat enough to paint details on that
could be as fine as 100-200 microns - ideal for fine details on faces, buildings and so on, often painting individual hairs.
This material had several advantages:
being quarter sawn, the grain runs across the panel as you can see from the image on the right. When wood absorbs water from the atmosphere,
the harder and softer parts of the grain absorb it differently and expand differently. If the grain runs parallel to the surface or at an
angle, the wooden panel will spoon, twist and otherwise warp which is wholly undesirable for a painting. However, if the wood has the grain
running across it, it will not warp.
This was known about in the 15th century and this is what the Flemish paintings were painted on at the beginning of the renaissance. However,
when the Italians started to have their renaissance, after Jan van Eyck had died, it was as though that had been forgotten about and they used
planks that had been cut across the trunk so the grain travelled through the panel in great arcs and when it changed its moisture content, it
In fact, the warping was so bad that in parts of the panel where the rings curved the most, they would cut that bit out and replace it with
a piece of wood that had a flatter ring structure in it.
The reason it is difficult to get seems to be that virtually all wood is cut simply in planks that go across the wood without regard to the
direction of the rings. To cut planks where the grain runs across the plank as in these pictures here, you need to cut the wood radially. Originally, it was produced by splitting the trunk radially so that you would end up with a set of wedge-shaped planks and if you look at the old Flemish paintings, that is exactly what they are painted on.
Getting hold of it
The fact that virtually all planks are just cut
across the trunk regardless of grain makes it easy and cost effective for the saw mills. However, if you want a piece of wood that is
going to last and not warp, you want the real thing.
Split radial oak is really something that if nothing else will do, you are going
to have to do it yourself.
Quarter Sawn Oak, however is available online and you can order as much or little as you like. These people don't do anything else and
they know what they are doing. I get my panels from them, they are The Quarter Sawn Oak
Company, based in Edale, Derbyshire (UK) and sell to DIY and trade.
This is a piece of untreated, planed all around, quarter-sawn oak panel that is roughly 10" x 12"
(25 x 30cm) and 9mm thick bought directly from them. In my experience, the company is helpful, delivers on time, is not expensive
and the wood they supply is excellent quality and the correct size.
This is a nice size to work with for doing portraits. As untreated, it is already smoother than canvas; when it is treated,
it is smooth to the level of a shine and you can put in an incredible level of detail with it.
All images and original artwork Copyright ©2017 Paul Alan Grosse.