'0' Always take care handling lead + cleaning tips.

It is poisonous - avoid inhaling any dust produced Always take care handling lead.
See why:- Working safely with lead.

"No safe threshold for lead exposure has been discovered—that is, there is no known amount of lead that is too small to cause the body harm."

And especially make sure you don't breath in the dust and wash your hands before eating!! *

Cleaning Lead.

Unfortunately cleaning can reduce the detail visible especially on old white lead as it is often the dirt which shows up the markings! It is worth taking an image of a lead seal after gently removing any obvious obscuring incrustations with an implement softer than the lead. However most need cleaning to see the detail below the dirt.
Unlike old bronze and copper, lead is fine to clean under the tap or even soapy water with a soft nail-brush, in fact it is probably the safest way to clean it as it stops any dust being produced. Just be careful not to deform it with any hard cleaning implements as it can be very soft.
I tend to wash all the obscuring deposits off and then highlight any markings by rubbing graphite over the surface with my fingers. Lightly apply pencil graphite and rub in with your finger tips to bring out the raised markings.
For hard white deposits (lime-scale) it has been found effective to place the seal in a glass with a layer of water softener de-ionising resin below and above it and pour boiling water on top. Do not leave for long as new lead is soluble in water.

* A description of Lead Mining in Somerset, 1667 by Joseph Glanvill and Others
"Those who live near where lead ore is washed cannot keep either dog or cat, or any sort of fowl, but they all die in a short time. And I have known of a little house wherein lead ore was kept some time, though afterward made very clean and well bedded with fern, yet when calves were put into it, they all died shortly after. And children sometimes in these houses have died suddenly. If any sort of cattle eat often of that grass, on which the steam, which rises from the smelting of lead, falls, they all die in a while after..."

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