[Ansteorra] Dogfish anyone?

C. L. Ward gunnora at vikinganswerlady.com
Wed Apr 14 23:22:53 PDT 2004

>Can you also please tell us which cultures used
>this rottenstone in the Middle Ages and when?

Not specifically - the earlier you go, the less evidence survives about how
wood items were finished.  For instance, in Viking contexts, we have wood
that survives because it's been in a waterlogged site - but that means that
any oil or varnish is usually long gone by the time it's dug up, and what
the archaeologists have to do for conservation usually wipes out any traces
that might have survived a millenium of burial and water-logging.

Where we start getting concrete information about "sanding" and finishing is
fairly late period, and there we have data because in a very few places
someone wrote it down.  All the materials, though, are easily available
everywhere, and we have better early evidence that various abrasives were in
use for metalwork that we know were also definitely used later for wood.

Rottenstone is a soft, weathered, decomposed siliceous limestone, used in
powder form as a polishing material.  Another term for this substance is
tripoli, and it is used as a metal polish as well.

Usually the primary "sanding" of wood was done with a powdered pumice stone,
then final polishing/fine sanding was done with rottenstone - and this
technique is still in use today for high-end finishes.  Both pumice and
rottenstone are used powdered, and usually mixed with linseed oil for use
(though I've seen modern woodworking books sugest paraffin oil, kerosene, or
even water instead). Rottenstone is softer than pumice and the particle size
breaks down easily under use, making it good for achieving smooth, final
finishes. It's particularly used today in fine woodwork and luthier-work for
the final "rubbing out" of a lacquer or varnish to achive a very high gloss.

L.F. Salzman in _Building in England down to 1540: A Documentary History_
(Oxford: Oxford Univ. Press, 1952) mentions "sanding" using rottenstone,
scouring rush (aka equisetum, horsetail fern, shave grass, etc.), or
dog-fish skin. On the latter, Salzman notes receipts for "hundysfishskyn for
the carpenters" (Westminster, 1355) and "j pelle piscis canini pro operibus
stall" (Windsor, 1351).

In the 11th century, Theophilus (_On Divers Arts: The Foremost Medieval
Treatise on Painting, Glassmaking, and Metalwork_. Trans. John G. Hawthorne
and Cyril Stanley Smith. New York: Dover. 1979) mentions polishing niello
using powedered pumice stone, polishing silver using "chalk" or rottenstone,
and also using shave grass (equisetum) to smooth wood and parchment.

For metal polishing, aside from Theophilus's recommendations above, he also
suggests jeweller's rouge. Jeweller's rouge is powdered ferrous oxide
(Fe2O3, hematite, red ochre), and was used in medieval pigments and paints.
I know big pieces of wax impregnated with jeweller's rouge were found from
the Anglo-Scandinavian excavations at Jorvik (York, U.K.). I don't know that
you can say for certain that the York find was being used for polishing
metal, but I'd tend to think so. Jeweller's rouge has been in use as a
polishing agent all the way back to stone age peoples.  I've seen
speculation that some knapped-flint utsensils were polished with ochre, and
it has been scientifically demonstrated that the Olmecs in the New World
were using jeweller's rouge to polish mirrors (stone, not metal).

There are many other abrasives that were used in polishing prior to the
modern stuff.  Some others I know I've seen mentioned include powdered
volcanic glass, diatomaceous earth, emery, flint, and garnet.


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