Not only is the wood block a convenient height it is not a heat sink like a large anvil would be.
As the bloom burns into it there is better support for the bloom and less likelihood of part breaking off.
Bloom on Wood Anvil
Blooms vary from solid metal to foam to iron bits floating in slag. Generally they are a mixture of all three.
A good drippy coating of slag helps reduce oxidation and increase weldability.
The first and immediate job is to consolidate as much of this as possible into one lump using the original heat.
Consolitation of the foamy metal requires gentle pats of the sledge rather than hard blows.
Holding back is actually harder than swinging full force.
Manipulating the piece that is rapidly changing in size and shape is also tricky.
Closeup of the bloom
When cool the bloom will look like a giant clinker or burned lump of iron.
From Darrell,
"What may be of interest to the smiths is the way you can tell the relative composition of the fresh bloom based on colour especially,
and texture to a certain degree.
Just like in a forge weld, the slag (weld flux) almost looks hotter than the metal when you first pull the mass out of the fire.
The slag very quickly cools, while the core of metal holds its heat.
In the image above, you can see the lacey slag material that sticks to the centre and to the left in the image by its cooler colour.
That surface had not been worked over when the image was taken.
A nice comparison is the right edge of the bloom, which had the loose material struck off at that point."
Much labor is required from this point to completely weld the bloom into a billet and force out excess slag.
Drawing out, stacking and rewelding the iron will make the grain finer and make a more uniform product.
The slag and fine scale inclusions are what gives wrought iron a wood like grain and make wrought different than a homogenous product like mild steel.
Viking Style Bellows used in previous smelts to prove the concept.
Video prepared by Darrell Markewitz for YouTube
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