Wednesday, 31 August 2011

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.



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.

11 comments:

  1. Really useful post, Lee. Particularly useful thoughts regarding the plastic and glass shelving for figures. And good tip regarding undercoating the base of the figure - although I'm guessing if the figure is based (superglue or epoxy) at the same time as its undercoated, it should be fine? Anyway, thanks again for sharing the research.

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  2. Man that's some detailed article Lee and a great post.

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  3. Great post Lee. Haven't noticed any problems in my fig's, some I have had for around 40 years, but this has always worried my somewhat.

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  4. Very informative post and happily hasn't happened to me yet. I'll be on the watch for sure.

    Christopher

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  5. I agree, a very good, informative post. I haven't experienced it yet, but have been priming my lead since 1972. We brushed it on in those days.

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  6. Lead rot is real. It can effect different lead alloys differently. I've had particularly bad results with old Falcon (US) made by Jim Parcella in MA. I've had many of his figures rot. I'm thinking the particular mix of tin, antimony, and other non-lead metals added to the problem.

    AJ

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  7. If you look at this photo: http://1.bp.blogspot.com/_9N7LA-10pYg/SNj7rH-qdtI/AAAAAAAAALs/CrFFW8AEdlY/s1600-h/French_AWI_005.JPG you can see some lead rot on the sword near the hilt and under the arm. I've since repaired and re-overcoated this figure to stop the rot.

    AJ

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  8. Fascinating and scary. I'd never heard of this before. Makes sense though.

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  9. I have never painted the underside of my miniatures, and wonder if I have consigned them to a corrosive grave?

    My only hope is that I die before my models do.

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  10. Very useful post and as definitive as I've ever seen.

    There likely are some chemicals in different glues, besides in paints and the metal mix itself, all of which will be trade secrets of the various manufacturers and we'll never know it all.

    Another solution good for the industry is to buy more, new ones, although that does not help with the nostalgia of the old beloved figures.

    I have heard of something like this process being possible with plastics too, but haven't seen it on some very old ones.

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  11. Brilliant article.
    I use bleach to neutralize any acids present - is this worth while?
    I had a whole tray of hobgoblins get lead rot from a citrus air spray I was using. Crumbled to dust. Very sad.

    Another thing that worries me is using MDF bases. Do they emit acetic acid? Will a layer of superglue Then a spray of gloss varnish Be enough to protect the underside of an integral base?
    Excuse the weird caps- using an iPhone.
    Thanks again!

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