Revisiting 'Lead Rot'

This 1984 Games Workshop Lizardman in my 
collection clearly shows the early signs of lead 
rot in the form of a white 'bloom'. 

Nearly a decade ago I wrote on this blog about the dreaded phenomenon known as Lead Rot. This supposed disease could eat its way through lead miniatures leaving nothing but dust in its wake. The subject has repeatedly come up for discussion on various miniatures forums over the years and recently I found some really old miniatures in my own collection that seemed to be exhibiting signs of this 'disease'. I decided it was time to dust the subject off again (excuse the pun) to stimulate the conversation and see if anyone else still has experience of this scary phenomenon.

Since I first wrote this article the miniatures industry has undergone a massive change in materials and manufacturing techniques meaning that very few modern miniatures are pure lead. Some manufacturers started changing the materials they used for casting miniatures as early as the 1960's however the biggest shift towards other materials took place in the early 90's and today most are made of white metal which is an alloy of lead and tin. so old lead miniatures generally (but not exclusively) pre-date this period. However I reckon most wargamers of a certain generation have at least some miniatures that are older than their kids (I certainly do) and these figures are therefore very likely to be cast from pure lead. 

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"A figure with lead rot is literally decomposing before your eyes." [Toy Soldier Museum]

In the forty 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?

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 the metal figure to be in contact with an 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)

This Electron Microscope image of corroded lead is 

enough to strike fear in the heart of any miniatures collector! 

Sources of acid can include PVA glue, enamel or oil based paints, and even some varnishes if applied directly to unpainted metal. Acid conditions on the surface of models can also be caused by the decay of organic residues such as the dead skin cells contained in household dust. Conversely the oils secreted by the skin can actually be beneficial to lead miniatures because they create a waterproof barrier on the surface blocking CO² from oxidizing the surface... so stroking your miniatures and talking to them is actually good for the little fellas!

Carbon dioxide is everywhere of course but CO² levels can increase in enclosed environments such as display cases. Storing miniatures in well ventilated locations does seem to help retard the chemical reaction as does the use of silicon desiccants to reduce moisture. However the simplest solution to prevent the ‘rot’ is to get painting! Once a model has been cleaned and 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.

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 release 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 do have a model that is showing signs of lead rot it is not too late to salvage the situation. Clean the surface of the model thoroughly but avoid anything acidic as a cleaning agent. 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 corrosion 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.

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I'd be interested to know if any of my readers have encountered 'lead rot' in their older figures, or indeed in any newer ones. Modern alloys should make this problem a thing of the past but I guess under extreme conditions it could still happen. Thanks in in advance for any feedback and have a good weekend folks.