Cleaning lead type

Alayne Alvis <alayne.alvis<-a t->sydney< . >edu< . >au> writes

>I have had an enquiry about cleaning lead type.  The person
>concerned is concerned about the toxicity inherent in any process
>that involves lead.  Would anyone with experience in this area be
>able to respond directly?

A number of comments here:

Do you want to preserve the ink in place as part of the history of
the object? If so, this limits treatment option.  If you do want to
keep the ink, I'd probably limit cleaning to brushing in tap water,
or, if the ink is non-soluble in ethanol, then I'd swab it in
ethanol to remove some of the dirt.

In cleaning of archaeological lead I have often used fine,
glass-bristle brushes.  The coarser glass bristle brushes visibly
scratch the surface of lead, but the finer ones appear to polish the
surface.  As the micro level they are still altering the surface,
but with archaeological lead, the surface is rarely pristine.  It
depends on how much original surface you have left.

DTPA is also commonly used as a chelating agent to remove lead
corrosion.  It works well, but as with all chemical methods, the
metal must be rinsed thoroughly (with tap water for lead, never use
distilled water or deionized water on lead) to remove any chemical
residues, which would promote later corrosion.

I have heard that deionizing resin is good for removing lead
corrosion, but I've never tried it myself.  This method might be
useful if you want to preserve the ink, but you'd have to test its
effect on the ink first.

I have tried lead electrolysis and had good results with it. There
the corrosion gets turned back into lead, so some of the losses to
the artefact can be restored if it was heavily corroded (although
the shape of the corrosion doesn't always return to the original
shape of the object).  Talk to the people at Parks Canada in Ottawa
about that, they have more experience than I do with that technique.

I wouldn't recommend cleaning with acetic acid as that is very bad
for lead, and you'd really have to remove even the slightest
residues to prevent further corrosion.  The chemical strippers are
also probably not necessary and probably damaging in the long run.
If you want to strip the ink off, 10% sulphuric acid might do the
job and would be better for the lead in the long run, so long as you
don't soak things in it (unless you've got the lead connected to
electrolysis).

After all of these treatments, the lead would have to be well rinsed
of any residues and thoroughly dried, either in solvents or with
heat.  With most of my lead treatments I have waxed the lead with
microcrystalline wax after, as an added surface protection.  The wax
is best heated into the surface and then the excess wiped off.

Valerie Tomlinson
Conservator
Auckland War Memorial Museum
Tamaki Paenga Hira
The Domain
Private Bag 92018
Victoria Street West
Auckland 1142
New Zealand
+64 9 306 7070 ext 7304


                                  ***
                  Conservation DistList Instance 27:31
                Distributed: Thursday, February 6, 2014
                       Message Id: cdl-27-31-005
                                  ***