The leading work on the subject of Blister Steel is K.C. Barraclough,
Steelmaking before Bessemer: 1. Blister Steel. If this is still in print it
will be available for the Institute of Materials.

The core of unconverted wrought iron was known as the sap. This results
from the iron not having been in the furnace long enough. You are not to
blame for having this happen, because you are probably the first people to
make blister steel since 1949.

Your inquirer in asking you to replicate medieval artefacts is committing a
fundamental error: Blister steel was a 17th century invention. It used to
be thought that it was an English invention, but Barraclough found it had
been invented slightly earlier in Germany. There is no reason to believe
that it was a medieval process. Furthermore, a particular kind of
converting furnace was used, and I think evidence of such furnaces would
have come to light if they were used before 1600.

I have reviewed evidence for 16th century steelmaking briefly in an article
'The cartel in oregrounds iron trading: the raw material for steel in the
18th century' Journal of Industrial History 6(1) (2003), 25-49. Such
evidence as there is concerning steelmaking in the 16th century suggests
that a different process was in use then.

I think your choice of early puddled iron was probably not the best (as you
realise). Most of the steel made in England between 1615 and 1855 was not
merely made from charcoal iron, but the Swedish oregrounds iron, all of
which came ultimately from ores from the Dannemora mine. The special
quality of this ore was that it contained manganese, which reacted with
impurities and carried them into the slag. A certain amount of 'Old Sable'
Russian iron was however also converted to make a less good steel. If you
do not have oregrounds iron available, rather more modern puddled iron might
actually have been better.

Steel was an expensive product. A relatively small amount of it was welded
along the cutting edge of an edged tool in the course of its fabrication,
the rest of the metal in the tool being iron. Blister steel is so called
because it has blisters on the surface. Not being a metallurgist, I am not
clear why blister steel was not considered suitable for making into tools,
but it was not.

Something like the process that you seem to have in mind was (I believe)
however used by the Birmingham 'toy' trade when producing steel 'toys'. Toy
in this context should perhaps be translated into the modern word trinket.
These were fabricated in iron and then case hardened by heating them with
charcoal, but no doubt for a shorter time than for blister steel, as it was
not necessary that the artefact should have more than a steel surface; at
least that is my understanding. The locks for flintlock muskets were
similarly made in iron and then 'hardened'.

I suspect that your archaeologist friends may be starting their argument
from an inappropriate point. If they are dealing with arrowheads, I would
have thought that the starting point was a metallographic examination of the
metal, which should provide clear indications, of what the metal consisted
of.

I would be interested to know what site they are interested in. Perhaps you
can persuade them to post a query on the Arch-metals list, to get a
discussion going about this.


Peter King

-----Original Message-----
From: Arch-Metals Group [mailto:ARCH-METALS@...] On Behalf Of
Steve Suff
Sent: 26 September 2003 14:29
To: Peter King
Subject: Blister Steel

We recently were asked to make some blister steel from wrought iron to
discover whether the process could have been undertaken at a medieval
ironworks that was being studied.

For the purposes of this task we used very early puddled wrought iron
(although charcoal wrought iron would have been used at the time). The
wrought iron was surrounded in charcoal and placed in a clay box which was
then heated in a furnace for 12 hours at 900-1000 degreee centigrade.

The results showed that steel could have been made with the technology
available at the ironworks during the period concerned.

However when subsequently looking at the photographs (which are posted on
http://uk.groups.yahoo.com/group/realwroughtiron/ ), it could clearly be
seen the depth of steel penetration which had been made into the iron,
leaving a wrought iron core. It occurred to us that given that the
technology was available, that it may have been used for weaponary, tools
etc. For example a large number of arrowheads could have been stood upright
in sand in a clay box to the level where a steel tip was required, the
exposed tip then being surrounded in charcoal and heated in the furnace.
Similarly, a sword or axe could be heated for a predetermined time to
ensure sufficient penetration to have a steel edge but retaining a softer
wrought iron core.

Technically, from a blacksmith point of view there seems little advantage
to fireweld a steel edge on the wrought iron to make such items and a
considerable advantage in time by using this method. If you estimate that
to fireweld steel into an arrowhead would take approximately ten minutes
and Robert Hardy estimates that one million arrows were used at the battle
of Cressy, the time saving would be over 3,000 man weeks (at a 50hr week).
As this approach struck us almost immediately when looking at the treated
bars and we were not even considering the subject it would seem to us that
smiths at the time could have reached a similar conclusion.

As we are neither weapons experts or armourers we do not have sufficient
knowledge or experience in this field to know whether this is a method that
was actually used but we thought it interesting enough for those that are
to consider this as a possibility.

Steve Suff
Chris Topp & Co