Reprise: Lead Rot, Myth or Reality

A couple of years ago I write a post about the dreaded phenomenon known as Lead Rot . This supposed disease can eat its way through lead miniatures leaving nothing but dust in its wake. The subject has repeatedly come up for discussion on various Miniatures and Gaming forums so I thought it worth revisiting this post and updating it where appropriate. I hope you find it useful.

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Source: Toy Soldier Museum

In the twenty odd years I've been collecting and painting miniatures I've heard lots of horror stories about Lead Rot. This 'disease' can allegedly eat its way through a whole collection like some ravenous B-Movie monster. As a painter I want my models to have the best surface possible on which to work. I certainly don’t want to see a well painted model disintegrate before my eyes. So, is Lead Rot a real problem or a mini painter’s old wives tale?

The first step is to try to understand what Rot looks like. Some painters describe powdery discolouration ranging from green through brown and grey. However the most common description is of in a whitish grey surface ‘bloom’. In severe cases the surface of a miniature can actually be pitted and rough to the touch. The picture above shows a catastrophic case of rot in three models (not my own, thankfully). As a collector this picture makes my toes curl but is this actually a disease or merely some form of corrosion? And once ‘infected’ can a model be saved?

1984 Games Workshop Lizardman

One explanation I read suggested that this was Lead rust. Iron rusts red and lead white. However this isn’t the case. Neither is it a disease or a fungus as has also been suggested. The white powdery bloom is actually Lead Carbonate and is in fact a chemical reaction, a form of corrosion that requires lead to be in contact with acid and carbon dioxide to act as a catalyst.

"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." (Source: Curator of Navy Ship Models)

(Source)

Sources of acid include PVA glue, enamel or oil based paints, and even some varnishes (if applied directly to unpainted metal). Carbon dioxide is everywhere of course but storing miniatures in well ventilated locations does seem to help retard the chemical reaction. Its worth adding at this point that most (but not all) modern miniatures have a relatively low lead content, being a pewter mix of one type or another. As such they are much less prone to this reaction than older models which were often cast from 100% lead. If, like me, you have a large unpainted mountain of models, it’s likely that some of them will be older types and therefore at risk.

So what can you do to prevent the ‘rot’ setting in? Get painting! Once a model has been sealed properly with an undercoat (don’t forget the underside of the base) then no CO² can get to the surface and the chemical process cannot begin.

Electron Microscope image of corroded lead (Source)

For display models try to use plastic or glass shelves rather than wooden ones. Wooden display cases with relatively stagnant atmospheres will create an acetic acid-laden micro-environment where lead artefact's will corrode even without being in physical contact with the wood. Hardwood's in particular emit more acetic acid than soft woods with Spruce, Pine or Elm being the 'safest' options. But even these can result in corrosion, especially if the wood is varnished or polished. Whatever display case you use maintaining good ventilation is essential to mitigating the conditions that can cause lead rot. (Source: Realm of Lead Addiction)

If you have a model that is showing signs of lead rot its not too late to salvage the situation. Clean the surface of the model but avoid anything acidic as a cleaning agent (one source I read suggested using vinegar!!!). Any areas that have pitting can be cleaned up with a needle file or for more severe damage removed with a craft drill. Once all sign of rot has been removed seal the surface with an undercoat of acrylic paint and then store in a dry environment until ready to paint. Then sit back and enjoy the fruits of your labor happy in the knowledge that your new ‘little friend’ will be around for some time to come.