[TheForge] Pure Iron and time

[George Dixon]

The displacement I referred to can be described as the bulge that occurs 
on the side of a bar of metal when it is very hot and struck with a 
hammer on its top.  Metal at its higher-end forging temperatures is very 
plastic, so when a hot bar is struck, the metal moves in a manner which 
it does not at lower temperatures. This bulging displacement is part of 
what can make a forging 'look soft'.  By comparison, nominal mild steel 
bar stock looks 'hard' in that it has stark lines, flat surfaces and 
crisp edges.
Pure Iron is more plastic at whatever temperature than is mild steel. 
 The soft bulging sidewalls and undulating surface results of hammer 
forging is more apparent in Pure Iron (or wrot iron) than in mild steel. 
 Pure Iron forges more like bronze than steel....without the unforgiving 
nature of hot bronze.

At lower temperatures, the core of a bar does not move under a hammer, 
but the outside of the bar does.  This is why a bar will shut at the 
end, as the outside moves more than the core.  At a red heat on down to 
room temp, the outside of the bar compresses, the surface becomes 
smoother and there is no bulging displacement.  This is why plannishing 
works at low temp but crisp lines and sharp edges are next to impossible 
to get at high temperatures.

A while back I did a reproduction of a 17th century German gate....small 
garden gate.   The smith who had made the original did not have the 
range of nominal stock we do.  So der kunstschmied took what he had and 
forged the stock sizes that the gate required.  It was wrot iron, which 
has to be forged at the top end of its heat range, white/yellow, or it 
splits.  This necessity to rework stock (to the required sizes) for his 
gate and the fact that the stock was iron meant that every inch of every 
bar was forged very hot and the soft displacement was the by-product of 
his necessity.  Today, there is no such necessity, but the look of that 
German gate's stock became a touchstone for what I want metal to look 
like in a project.  So I either use Pure Iron or I get mild steel very 
hot and rework every inch of bar or plate or sheet (with a hand hammer, 
the face of which has a very slight crown) to achieve that effect. 
 Sheet and plate, worked through a hot coal fire, then hand sanded is 
very nice to look at.


George Dixon
("wrot" is how wrought was spelled on some late 19th and early 20th 
century drawings and references...for what that's worth)