How DENSE are you? Measuring Blooms

20 years

90 personal bloomery iron smelts

Ya, I have a few blooms kicking around...

Like about 30 

(not counting smaller pieces, blooms now rendered down into bars)

During the early years, working with Lee Sauder and others at the annual Smeltfest workshops, typically individual smelts were in the 45 kg range, which in turn resulted in blooms at 8 + kg. 

Tests done here in Wareham (where accessing ore was a problem) more typically ran 25 to 30 kg ore, with resulting blooms averaging between 2 - 5 kg. This primarily because we figured if you could make a medium sized bloom, with more ore and time you could certainly make a larger one. 

Another reason was simple handling of the blooms themselves. There is a physical limit to how much impact force (largely untrained!) workers can apply with hand sledge hammers. Even historically, once blooms got much over about 5 - 8 kg, they were cut up into smaller chunks to allow effective compaction into the finished iron bars.

So 

Something I was told at the 2008 'Iron in Thy' symposium always has annoyed me. As it did the other working participants sitting around that table :

'Modern experimenters are unable to produce iron blooms of similar quality to those made by the ancient iron masters'

At the time, I certainly felt still fairly new to bloomery iron smelting, to the point I just felt I was staring to get some handle on the methods. (I would have been at numbers 33 - 35 at that event). In 2008, I did not feel I had enough direct experience, and certainly not any hard numbers, to refute that sweeping statement.

Obviously, even a dozen years later, that statement (from a well known archaeo-metallurgist) still sticks in my craw.

Generally, all the blooms produced here at Wareham are 'finished' to the same level, which does help make some comparisons valid. Given the small working team, with normally only myself as having any blacksmithing experience (1) we hammer work any bloom through only the heat available at extraction. This involves knocking off any clinging slag, then very rough compaction to force loose exterior into the core. As temperatures are rapidly dropping while this is happening, there is rarely any actual welding taking place, more mechanically pressing out larger voids and forcing out still fluid slag. 

Starting in 2012, there was a 30 ton hydraulic press available at Wareham (modified log splitter). In some cases, after the initial hand hammering, blooms were rushed to the workshop and the mass was given several compressions, then cut via the press.

So over the last two weeks, I have pulled out the blooms on hand here.

Each was re-weighed (to differing methods, depending on overall size)

Three different containers were used for volume by water displacement. 

There certainly will be accuracy limits determined by the simple equipment used. Water measurements at best accurate to 5 ml within 1000 ml. Larger blooms, over 6 gm, weighed with a scale +/- 5 gm

The overall intent here is to compare these measurements against densities published for some artifact blooms, one problem being that sample size is considerably smaller.

Preliminary results :

Wrought Iron (solid bar) = density of 7.75 gm/cc (2)

Bloom Average (28 samples) = density of 6.28

This actually compares very favourably to artifact blooms, at least the few I have found with descriptions of density. I will be trying to contact some specific museums to see if they can provide numbers on their artifacts.

1) Neil Peterson has been slowly increasing his skill and knowledge of working blooms specifically. Neil has been coming up and undertaking afternoon workshop sessions were he has been taking pieces in the 500 - 800 gm range and compacting these down into finished working bars. I should be noted that this still is different than sledge hammer work - Striking is it's own separate skill set (and one that I also have rarely done!)

2) https://www.engineeringtoolbox.com/metal-alloys-densities-d_50.html