Pete,

Many thanks - I have a clearer idea of what your furnace looks like now.

I think it's almost certainly a roasting furnace.  Schnabel's Handbook of 
Metallurgy refers to similar furnaces with bottoms consisting of a flat 
grate and a depth of ore of about 1-5 ft deep held in a shaft typically 4 ft 
square.  The only air supply is natural draught.  He says that they were 
used for roasting copper ores, lead ores and specialised types which 
collected the gases were used for burning pyrites.  The designs varied and 
were either batch processes or the grate bars were triangular and if rotated 
enabled the kiln to operate continuously.  A limekiln would be a somewhat 
cruder approximation to one of these.

Was it used for smelting?  I think unlikely but the design should give you 
the answer.  If there was a floor underneath the arch, similar to that of a 
lime kiln, then it's more probable that it was a roaster.  If it was used 
for smelting, it would have some means of catching slag and metal and 
separating the two.

Don't be put off by the glaze on the walls, a roaster is just as likely to 
have lead glaze as a smelting furnace (and probably more so)  All the ruined 
roasters which I have seen are glazed.

Regards

Richard Smith

----- Original Message ----- 
From: "Curator" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Sunday, May 10, 2009 1:41 AM
Subject: Re: Lead smelting


> Thanks to the various people who responded to my email. Individual replies 
> are below:
>
> Tony Brewis
> Thanks for that, the figure you refer to does seem to represent an older 
> form of what I am talking about.
>
> Richard Smith
> I am aware that good deal of shaft smelting has taken place but the vast 
> majority seems to have used an air blast of some sort. The furnace on Sark 
> (well done Howard!) didn't use an air blast, just natural ventilation. The 
> interpretation isn't mine, I should add, but from Bryan Earl, who knows 
> much more about this sort of thing than me. I wasn't aware of this sort of 
> process before. The structure dates from about 1840.
>
> Mike Gill
> From the above you will gather that it is most likely a French design. 
> Unfortunately there is almost nothing left in Cornwall in the way of 19th 
> century lead dressing sites or smelters but I'm pretty sure nothing 
> analogous was built here. I'm not sufficiently up with Continental 
> archaeology to know if anything similar still exists over there.
>
>
> I presume that this was a simple process of charging the shaft with ore, 
> fuel and flux, if any, then letting the molten metal dribble down into 
> moulds, like a blast furnace but cooler. The problem with Sark is that we 
> don't really know much about how much ore the mine produced, but I guess 
> they had enough to do something with it.
>
> Thanks again everyone.
>
>
> Pete
>
>
>
> ----- Original Message ----- 
> From: "TONY BREWIS" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Saturday, May 09, 2009 3:08 PM
> Subject: Re: Lead smelting
>
>
> As a miner, I am somewhat out of my depth here, but are the shaft furnaces 
> for lead
> being talked about similar to these illustrated in the1556 publication De 
> Re Metallica
> by Georgius Agricola?
>
> Stephen Henley has scanned these and put them on a website. I find it 
> difficult to get
> to it directly, but on Google, going to sites in the UK and asking it to 
> search for
> stephen henley agricola, it comes up as top of the list.
>
> Look at  the illustrations from Book 9. Number 13 shows the furnaces I am 
> talking about.
>
> Tony Brewis