The plague of disintegrating diecasts

There seems to be a growing epidemic in recent years of diecast models simply crumbling to dust for no apparent reason, leaving many collectors perplexed and upset at the loss of a model through no fault of their own. Known variously as 'metal fatigue', 'zinc rot' or 'zinc pest', this is caused by impurities of lead and other metals in the zinc alloy used in diecasting and should be avoidable with modern production methods, but sadly it seems even expensive high-end models are not immune from it and there is no cure once it has taken hold.


Zinc pest is not a new problem by any means and was reportedly identified as long ago as 1923. Pre-war Dinky Toys are particularly well known for suffering from it, allegedly because metal shrapnel was swept off the floor and put into the melting pot along with the metal foil from old cigarette packets and goodness knows what else, and this is why some early Dinkies are now so rare and valuable. Improvements in quality control and purification methods in the 1960s mean toys and models produced since then should be largely immune to the dreaded zinc pest but recent experience suggests this is not the case and the consequences of an impure batch of metal used some years ago are now starting to show themselves.

Brittlebus indeed. Touch a fatigued model and this can happen!

I have fortunately had little direct personal experience of zinc pest but it is starting to spread among models made in the 1990s and 2000s and there have been regular reports on the various internet groups of collectors making the unpleasant discovery that one of their models is affected. Britbus models have been notorious sufferers for some time, which has led to them being nicknamed 'Brittlebus', but it has more recently spread to EFE and Corgi products too. The models will appear perfectly fine when they leave the factory and will pass all quality control checks, as the chemical reaction caused by the impurities takes a long time and often the symptoms won't become apparent until a decade or more after manufacture. Although high humidity accelerates the process, the way the model is treated has no effect so careful storage in darkness and away from extremes of temperature unfortunately isn't going to make any difference and any model made from sub-standard metal is doomed from the start.
   
Imperfections in the paintwork such as a crazed effect, bubbling or flaking are often the first sign of zinc pest and indicate that all is not well underneath the paint. When the disease reaches the next stage the metal will start to swell and distort, and in the case of model buses this often causes one or both sides of the body to bulge outwards, which is not a pretty sight. It will now be extremely brittle so even the slightest touch is likely to result in the entire body either shattering into pieces or simply crumbling into a cloud of dust, both of which are very unpleasant experiences. On examining the remains, the inside of the metal will often have a dull and porous appearance where the contamination has occurred, and some of the affected models do feel unusually light and insubstantial as a result of this porosity.

Cracking and distortion everywhere. A horrible sight and completely beyond repair.

Sadly there is nothing whatsoever that can be done to repair the damage caused by zinc pest or even to stop it spreading further, as there has been a chemical change deep within the metal and by the time it becomes visible it is already too late. Once your model shows the first signs of the pest it is basically scrap and all you can do is salvage the plastic parts for use on other projects, try to obtain a replacement model and hope it doesn't suffer from the same problem. Models from the same production run are likely to have been made using different batches of metal, so some will be unaffected while outwardly identical ones will suffer and it is impossible to tell when buying one. Because it takes so long to manifest itself, it is still too early at this time to know if any of the more recent generation of models are susceptible to the dreaded zinc pest, so all we can do is wait and hope they aren't.

The loss of a cheap toy to zinc pest is one thing, but losing a collectors' model you may have paid a significant sum for is quite another. You might think it is more prevalent among cheap models as the manufacturers save money by buying cheap contaminated metal, but the cost of the model seems to have no bearing on the likelihood of zinc pest as even some high-end 1/18 scale model cars that retail for three-figure sums are not immune from it, and the unstoppable deterioration of something that cost so much must be soul-destroying. There appears to have been a bad batch of metal that unknowingly did the rounds of the Chinese casting factories some years ago and the consequences are now starting to make themselves known long after it was used. 

This was a mint boxed model until the zinc pest set in. Now it's only fit for scrap.

This list is by no means complete but these are some of the models known to suffer from destruction by zinc pest. If you know of any others not listed please let me know.

• Britbus: Scania OmniDekka, Leyland Atlantean, MCW Metrorider and Metropolitan, Dennis Loline, Alexander R-type, Guy Arab
• Corgi OOC: MAN/Volgren, Bristol FS, AEC Q-type single-deck, Weymann trolleybus
• EFE: Leyland PD2, Bristol RELL, Alexander Y-type, RT/RTL, Atkinson lorry
• Creative Master Northcord: Alexander ALX400 open-top, Alexander Dennis Enviro400
• 80M (Hong Kong): Volvo Olympian Rickshaw Bus
• Vanguards: Morris Marina, Ford Transit van
• Oxford Diecast: AEC B-type bus

The warning signs:

• Crazed, flaky or bubbling/blistering paint
• Cracks in the metal
• Swollen, bulging and distorted parts
• Parts easily breaking off
• Unusually lightweight feel to the model

Watch out for any of these things happening to your beloved models. Zinc pest is very bad news but there's absolutely nothing that can be done about it - it only strikes after many years and will inevitably destroy any model it affects, so buyer beware! It seems likely that within a short time certain models will become very rare and sought-after as so few will escape the ruinous effects of the dreaded zinc pest, and I fear this is just the thin end of the wedge and many more will reveal themselves as sufferers over the next few years.