With all due respect for Professor MacKay's experience and suggestions for
cleaning the Mesoamerican pottery I must challenge the technique and say
please don't use it.  My reasons are as follow's:
 
1. Much Mesoamerican pottery has calcareous (calcium carbonate) inclusions in
the clay or temper and these will be dissolved out by hydrochloric acid (HCl).
2. If you have fragile paint or slip on the surface the bubbling will dislodge
it from the artifact.
3. HCl reacts with iron in the artifact making it soluble, dissolving some of
it out and moving around more of it.  If you have a light colored object it
canleave yellow stains.  It may affect later analyses.
4. The use of any acid on "insoluble" concretions turns them into water
soluble salts.  Any left in or on the artifact can eventually crystallize
at or on the surface of the object when the humidity drops (like next winter)
and again damage the surface or in the worse case destroy the whole fabric of
the artiface.  The water soluble salts can be soaked out but the success of
the soaking must be monitored.
 
I do not feel that acid cleaning of ceramics should never be done.  Mostly
because so far there are not good alternatives developed.  However, the use of
acidshould be carefully considered and carefully monitored.
 
A lot of work has been done on the cleaning of ceramics since 1960.  If people
are interested I can post a bibliography on the list or contact me directly an
d I'll send it too you.
 
Jessie Johnson
Conservator, Gordion Excavations, Turkey
Texas Memorial Museum
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