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?
>
>Most of the type is lightly encrusted with lead oxide, plus a
>hundred years of ordinary dirt and remnants of printing ink.  He was
>considering:
>
>    A rinse in soapy water to loosen the dirt
>
>    A soak in an organic solvent--a dilute solution of citrus paint
>    stripper, N-Methyl Pyrrolidone, which is completely
>    water-miscible, to loosen the ink
>
>    A soak in 5% acetic acid to dissolve the majority of the lead
>    oxide followed by some time in an ultrasonic bath to finish the
>    job
>
>He also had a couple of questions:
>
>Do you think this set of actions will do the job and bearing in mind
>the toxicity issues is it safe for me and for the type?
>
>Should the solution in the ultrasonic bath consist of plain
>(distilled, perhaps?) water, or is there a better alternative?

Cleaning the type with soapy water is fine by me as is the organic
solvent, as long as citrus paint stripper refers to its odor rather
than it containing any citric acid.  I would strongly recommend not
using the acetic acid solution.

The problem with the acetic acid solution is that you'll be removing
the lead oxide but at the same time you'll be producing lead
acetate, which is basically replacing one whiteish cover with
another one.  I'm not a big fan of chemical immersion baths, the
outcome is hardly controlable and there will always be chemicals
left in the pores of the metal or the produced surface (in this case
lead acetate), no matter how thoroughly you rinse it--just think
about the desalinisation baths used in the archaeologic
conservation, which take months to get a good result.  Acids
especially tend to leave some salts somewhere and it is just a
matter of time (and humidity) for them to start reacting again.

If possible, try to "sand blast" it with low pressure (probably
around 1.5 - 3 bar) and finely ground walnut shell (very light and
soft material; tried it on tin and it works well, never did on lead
though).

You might also consider not removing the lead oxide and instead
applying some microcrystalline wax (PolarWax) solved in white
spirit.  There is a good chance of the lead oxide becoming
translucent in combination with the wax.  Also the wax acts as a
mid-term conservation coating and can be polished to any desired
grade with soft brushes.

If you remove the lead oxides, please do the environment a favour
and collect all waste (including any solutions) and get them to a
waste processor.  Here in Germany the public waste disposal system
has certain centers you can drop small amounts of harzadous waste.
I'm sure you have something like that in your country as well.

Regarding safety: It should be sufficient to wear rubber gloves (and
dispose them with the other waste) and a tight fitting rubber mask
with a fine filter.  Do not use ordinary dust masks!  If possible,
work under a fume hood or a vacuum of any kind, that is properly
filtered (not a houshold vacuum cleaner, the dust ist too fine and
you will disperse it in the room).

Alex Grillparzer
Grillparzer Restaurierung
Kreillerstr. 13
81673 Munchen
Germany
Mobile: +49 157 714 50 416


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                  Conservation DistList Instance 27:31
                Distributed: Thursday, February 6, 2014
                       Message Id: cdl-27-31-006
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