Ken Hamilton asked:
"A friend of mine studying her family history keeps coming across   
copperus works, and has asked me what copperus is. Embarrasingly, I don't   
know, except that you use it to make black dye for textiles, and it has   
nothing to do with copper. Is there any more information on its   
source/method of production/uses? Has it a role in pottery making at all   
(one pottery round Denholme was famous for its black pottery, and is next   
to a copperus works)?"

The following short note which Michael Leach provided me for Essex   
Archaeology and History News, the newsletter of the Essex Society for   
Archaeology and History might be helpful:

"'Industrial Archaeology News' (Spring 1999) reports an excavation by the   
Canterbury Archaeological Trust of a late sixteenth or early seventeenth   
century copperas works  near Whitstable in Kent. It notes that no   
comprehensive history of this forgotten industry has been written. The   
raw material was iron pyrites (or "fool's gold") which is found as   
nodules in the London clay of the Thames basin, particularly on the Essex   
and Kent coasts. It is also found in Dorset and north Yorkshire, where   
the industry also flourished in the past.

Philip Morant (an 18th century historian of Essex)  noted the presence of   
this industry at Brightlingsea where there was 'a House for extracting   
Copperas', and at Walton 'here is a famous Copperas house'. Both are   
marked on the 1777 Chapman and Andre map of Essex. A contemporary   
geographer noted at the foot of Beacon Hill, Harwich, that 'the stone   
along this shore is, much of it, of the Copperas kind, and a great deal   
of this mineral is found betwixt this and the Naze ... And hence, and at   
Walton, adjoining to the Naze, are several works for preparing and   
boiling the Liquids which produce, at last, the Copperas itself".

The process was lengthy, noxious and dangerous. Nodules of iron pyrites   
(ferrous disulphide with traces of other metals, including copper, cobalt   
and nickel) were collected from the shore and placed in huge clay lined   
timber tanks. Those at Whitstable were about 12 feet deep, 15 feet wide   
and over 100 feet long, and one works had seven of them!  After several   
years of exposure, a liquor containing a weak solution of sulphuric acid   
and ferrous sulphate was obtained. After collection in a separate   
container, the liquor was transferred to a lead lined tank for prolonged   
boiling (up to 20 days). Large amounts of scrap iron were added to   
increase the yield of the end product, ferrous sulphate, known at that   
time as copperas or green vitriol. After boiling, the concentrated liquor   
was run into a cooler, where crystallisation of the copperas was   
encouraged by placing bundles of twigs in the tank. The resulting   
crystals were removed, heated to melting point and cast into blocks for   
transport. The main uses of copperas were in dyeing and tanning, but it   
was also used for ink making and as a sheep dip. Sulphuric acid was a by   
product, for which there was increasing demand from new processes   
generated by the Industrial Revolution in the eighteenth century. The   
copperas industry rapidly collapsed and disappeared in the early decades   
of the nineteenth century, destroyed by new technology and cheap imports.

As the raw materials were to be found on eroding coastlines, many of the   
former copperas sites have disappeared into the sea. However, remains of   
a large timber structure were recently exposed at Tankerton, near   
Whitstable, and excavation confirmed that these were the remains of the   
tanks and jetties associated with a copperas works. It was a sizeable   
industry in its time, with a heavy capital outlay on plant and fuel. It   
probably relied on casual labour, mainly women, to collect the nodules of   
pyrites. In north Yorkshire, it was associated with the extraction of   
alum (also used in dyeing), another coastal industry using a similar   
technology of concentration of a liquor by boiling, followed by   
crystallisation.
A fuller article on this forgotten industry is promised in a future issue   
of Industrial Archaeology Review."

Paul Gilman,
Heritage Conservation
Essex  County Council


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