James,
    Your post sounds like a concise, brief summary of iron working in the
late 18th and early 19 centuries.  I would like to learn more about
recognition of things such as hammer scale, fayalitic slag, etc.  Is there a
source or series of sources you could post to the list which would bring
those of us only vaguely familiar with the process, products, and
by-products up to speed (or at least closer)?

    Chris Murphy
    Augusta State University



James Brothers wrote:

> Some basic terms.
>
> If you are converting ore to metallic iron you are smelting. This is
> either done in a bloomery (which is a batch process and results in
> low carbon iron, sometimes called wrought iron) or a blast furnace
> (which is a continuous process and produces high carbon iron,
> sometimes called cast or pig iron). At least in terms of historic
> technology. Later you get open hearth, etc.
>
> If you are removing either carbon or silicon from iron you are fining
> or refining it. Before 1783 this is done in a finery forge. It is
> possible that you might find a potting and stamping mill earlier than
> that, but the general consensus (which could be wrong) is that
> potting and stamping really never caught on in North America. After
> 1783, but usually not until well into the 19C, this would be done in
> a puddling furnace. You can also have something called a run out
> furnace.
>
> Assuming that you 19C smithy used coal and not charcoal you might be
> collecting clinker (coal residue), not iron slag.
>
> Generally the following is true. A bloomery will have ore, charcoal,
> and low carbon iron. You will also find fayalitic slag, hammer scale,
> and mossers or skulls (what is left in the hearth at the end of the
> day). A finery will not have ore, but will have pig iron, as well as
> hammer scale, fayalitic slag, and mossers/skulls.
>
> According to a number of sources, most good smiths could bloom. As
> what they produced was low carbon to begin with they would not have
> needed to fine it. They would have to consolidate the bloom and would
> want to fagot or pile weld it to end up with a piece that was
> relatively free of slag and homogenous.
>
> In the Adirondacks in the mid to late 19C the American bloomery
> process is used. This includes hot blast and results in a much lower
> iron content slag.
>
> James Brothers
>
> On Apr 25, 2006, at 11:44, Marty Pickands wrote:
>
> > I collected a fair amount of slag from a 19th c. blacksmith shop in
> > Parishville, St. Lawrence County, NY, in hopes that I could compare it
> > with slag from the small bloomery once located at the other end of
> > town.
> > Local tradition says that the other smith in Parishville was refining
> > this ore in his own shop after the bloomery shut down, and it would be
> > useful to know whether my smith was doing the same. Does anyone
> > have any
> > suggestions for kinds of tests I might use?
> >
> > Marty Pickands
> > NYS Museum
> >
> >>>> [log in to unmask] 04/24/06 6:20 PM >>>
> > Best place to start is Robert Gordon's American Iron (Johns Hopkins
> > 1996). It has a good chronology of how things were made and the
> > results. If you don't own a copy, you should. Bob has also produced a
> >
> > number of papers and a couple of other books on various aspects of
> > the iron industry (including slag analysis). If you want something a
> > bit smaller, and I think quite good (I wrote it), look at "Blast
> > Furnace, Forge, and Foundry" (pp 335-353) in Uplands Archaeology in
> > the East: Symposia VII & IX (available from the Archeological Society
> >
> > of Virginia). I also have a 70 page bibliography I'd be happy to send
> >
> > you (as I wrote my MA on the Virginia colonial industry it is a bit
> > heavy on that, but covers the US/UK up to 1900). If you want to do
> > research your problem will be getting references. Very few libraries
> > have anything, expect to use inter library loan a lot.
> >
> > There is not a great deal on slag. Unfortunately many archaeologists
> > don't even collect it. And if they do they seldom ever either
> > describe it or have it analyzed. It is commonly mischaracterized as
> > "clinker".
> >
> > Almost all blast furnace slag is glassy. But it can take on different
> >
> > textures depending on how it was cooled (the Us Govt produced a book
> > on how to do this in the 40s). This is because it is, for the most
> > part, a silica-lime glass. Lime is used as a fluxing agent. Generally
> >
> > it is green or gray green, but other colors are possible including
> > blue, white and red (it all depends on what is in the ore).
> > Regardless of whether or not it is hot or cold blast, charcoal or
> > coke, it will still be glass and glassy. If it is tapped out onto a
> > surface containing a lot of moisture it will be full of airholes. If
> > it is cooled quickly it will tend to look stoney. But regardless it
> > is still chemically glass. Batso, after it stopped making iron, used
> > the slag pile to make bottles.
> >
> > Finery and bloomery slag are not glass, they are fayalitic (Fe2SiO4).
> >
> > And may contain up to 70% iron. The bloomery process is "self
> > fluxing" and it is the iron that makes the slag liquid. Bloomery slag
> >
> > will often contain chunks of charcoal and unreacted ore. Finery slag
> > may contain chunks of charcoal. Both are usually dark brown to almost
> >
> > black and have a ropy texture.
> >
> > Foundry slag is also different, but I really haven't seen much. As I
> > remember it may have an almost metallic look to it.
> >
> >
> > On Apr 23, 2006, at 22:49, Ben Ruset wrote:
> >
> >> Hi All:
> >>
> >> I'm in the process of writing an article on the bog iron industry
> >> in the New Jersey Pine Barrens for my website, and had a few
> >> generic questions related to blast furnaces, forges, and slag. If
> >> someone can point me to some good source material, or even answer
> >> my questions, I'd be much indebted.
> >>
> >> Firstly, there is definitely a difference in the type of slag that
> >> is produced by a blast furnace and a forge. Within the scope of
> >> furnace slag, it appears that the slag is different depending on
> >> whether the furnace used the cold blast method, or the hot blast
> >> method. From my understanding, cold blast furnaces tended to
> >> produce very rocky, metallic slag that in some ways resembled
> >> pyrite in texture and form. Hot blast furnaces produced slag that
> >> is almost glass-like. Is my assumption correct?
> >>
> >> Forge slag seems to look just like you would expect a pool of
> >> cooled iron to look like. It is smooth in texture, without a lot of
> >
> >> visible impurities (ie: no unburnt charcoal, etc.) Are there other
> >> ways of telling if forge slag is in fact forge slag?
> >>
> >> I have seen varieties of cold blast slag and forge slag, and what I
> >
> >> assume to be hot blast slag, although it was at a site that I was
> >> unaware used hot blast technology.
> >>
> >> Secondly, when it comes to forges, it seems that many had both a
> >> stamping mill as well as a tilt hammer. The thing that I am unclear
> >
> >> on is what the main difference in the finished product of both
> >> were. I have scoured "Early Forges and Furnaces in New Jersey" but
> >> it is pretty unclear to me what the main differences are. If
> >> anybody can shed some light on the subject, I'd really appreciate
> > it.
> >>
> >> Thanks!
> >> Ben Ruset