The cleaning of stone tools procedure used with this method is to wash
the tools with detergent and water to remove dirt or soil deposits. To remove
deposits still adhering to the tool an ultra-sonic tank is used for 10 minutes
with the tool immersed in distilled water. The ultra-sonic tank will remove
such things as soil particles embedded in hollows in the tool. Caustic chemicals
advocated by Laurence Keeley (Keeley
1980, 3) and some other analysts, are not used for cleaning for the
following reasons.
1) Microwear analysts have compared prehistoric tools that have been chemically
cleaned with those that have not, and found that the polishes are not significantly
changed (Moss 1983, 105).
2) Experiments using the least caustic of these chemicals (NaOH) for only
10 minutes in a dilute solution, have shown that even such relatively mild
chemical treatment may visibly alter the surface of an unused flint.
3) The question of how much polishes are made up of deposits of the worked
material has not been definitively answered (see Vaughan
1985), so that deposits, for example of bone, may be one of the constituents
of polish, and chemical cleaning will remove this. Keeley even suggests
that the change in the appearance of bone polish after chemical cleaning
is due to the removal of bone apatite (Keeley
1980, 43). If such deposits are preserved on the tools it would be preferable
to develop techniques of residue analysis to identify positively the worked
material. The recent investigations into the use of blood residue analysis.
(Loy 1983) demonstrate that if such
deposits do survive, chemical cleaning could be destroying potentially valuable
information. Materials such as antler and bone, if they survive at a site
and they are a constituent of polish, will also survive on tools and be
susceptible to residue analysis.
If chemical cleaning is not used there is the
problem of organic residues on experimental tools that remain even after
washing and the use of the ultra-sonic tank, residues produced by the working
of green wood are particularly troublesome and remain in some cases even
after the tool has been cleaned in white spirit, which removes mastic used
for the hafting of tools. This problem is particularly relevant to tools
used in blind tests, as the presence of a residue from wood working could
enable the analysts to make a correct identification of the worked material
from evidence that would not survive archaeologically. (see
example) To overcome this problem experiments with biological cleaning
agents have been carried out and it was found that ordinary household washing
powders that contain enzymes remove such organic deposits very efficiently.
Simple immersion for 10 minutes in a solution of a biologically active washing
powder removes not only residual deposits, but also cleans off such things
as grease and any plasticine that may have adhered to the tool when it was
mounted for observation through the microscope. (see
example)
Cleaning of the tool's surface during microscopic observation is carried
out by wiping the surface with a cotton bud dipped in alcohol. Periodic
cleaning with alcohol is necessary for removing deposits such as finger
grease that are produced from handling the tool. The use of cotton buds
can sometimes produce false striations, when grease or remnants of plasticine
are present on the tool. The wiping action can spread such residues in one
direction giving the appearance of linear features, and so it is necessary
to be aware of this. A rotational action of wiping avoids this confusion
as if such false features are produced they become obvious from such a rotational
action. If such residues are shown to be present on the tool, it should
be removed from the microscope and re-cleaned following the procedure described
above.