Curator of Navy Ship Models – Lead Corrosion in Exhibition Ship Models.
I saw a link recently (the one above) to the NAVSEA Warfare Centers, Caderock Division which was of particular interest to those of us that share a passion for wargaming and military modelling. Whilst the article refers to Ship Models, the comments in the article refer just as equally to the collection of toy soldiers and wargaming figures and models of any genre.
So many early figures and models contained varying quantities of lead in different alloy mixes that those older wargamers and modellers amongst us will surely still have some in our collections.
The article talks about lead corrosion and notes that
Corrosion may be so severe as to completely consume the piece, leaving behind a white or gray residue popularly, and aptly, called “lead disease,” “lead rot,” “lead cancer,” or “lead bloom.”
The article goes on to look at how the corrosion occurs and what can trigger the corrosion. The actual chemical process of the corrosion is:
The chemical process is: Acetic and some other acids, in the presence of carbon dioxide, catalyze with lead to produce lead acetate and lead hydroxide. Lead acetate and lead hydroxide together react with carbon dioxide and form lead carbonate. Lead carbonate then releases acetic acid and the process becomes self-sustaining. It is important to recognize that the formed lead carbonate is not just a substance clinging to the surface of a casting, it is the surface of the casting transformed to powder. For practical purposes, a portion of the lead is gone and lead carbonate is left in its place. The lead carbonate releases acetic acid which can continue the process until the lead part is progressively consumed from the outside, inward.
The article notes further that the wood is one item that contains acetic acid – more so in the end grain than the edge grain even. Many models are stored in display cases built from wood and perspex or glass. This means the atmosphere in the case does not change often (the air goes stale) so there is likely a build up of the acetic acid in there and then once the chemical reaction starts, it just keeps going until the lead is consumed.
With regards to which woods are most harmful, the article lists different types of wood but goes on to note:
Nevertheless, a general rule of thumb can be applied: Hardwoods emit more acetic acid than soft woods. But any wood will fall into at least the minimally harmful category
The article also notes the other materials that may contain acetic acid, amongst a long list are also included the following:
- PVA glue or “white glue”
- Contact cement
- Plastic wood
- Latex varnish
- Natural varnish
- Polyurethane varnish
- Enamel paint
- Oil-based paint
- Pebbles and sand (unwashed)
I use balsa wood for many of the bases of my figures – balsa is (believe it or not) a hardwood. I also mix PVA glue with water and acrylic paint to coat the bases of figures. I then usually spray varnish with a polyurethane varnish. I’m hoping that as more modern figures have become lead-free that I no longer have any lead based figures in my collection but I will be examining the figures closely next week at mum’s as I have had them stored with little or no air movement for a couple of years now.
The article also notes a modelling suggestion from the Internet and states:
One treatment suggested over the Internet to modelers was to wash parts in vinegar to neutralize the lead carbonate. While this treatment may facilitate cleaning the affected parts, obviously the vinegar wash itself may attack the lead until it is neutralized by liberally rinsing it in water. Thorough removal of lead carbonate from within the model’s micro-environment is recommended, but we would suggest simply brushing it away. Although basic lead carbonate does not dissolve in water, mechanically rinsing corroded parts in running water would be preferable to applying more acetic acid to the piece. Wear a respirator when disturbing dry lead carbonate dust and be sure to wash your hands after handling lead fittings or lead corrosion byproducts.
Whilst newer castings, and certainly those of the last 10 to 15 years or so are generally lead-free, the article is a very instructing piece worthy of reading. Best of all, it seems, one of the recommended methods preventing or reducing lead corrosion is to change the air around the model – so take the figures out of the boxes, put them on the table, play with them and reduce the chance of lead corrosion in the older models.