By Maz Woolley
Photographs by Jane Jones, a member of the Oxford Diecast Collectors Facebook group. Text copyright of the Author and Jane Jones.
I make no apologies for returning to the subject of intergranular corrosion as it still seems to be affecting models from major diecast firms. Collectors looking at stored models have come across models falling to bits from time to time, The Corgi Vanguards Transit Castrol van has a tendency to self-destruct as shown in MAROnline previously by Dave Turner. Whilst Photoetched parts popping on resin models can usually be remedied with glue and care intergranular corrosion has no cure. Some people have stabilised the models by flooding them with super glue and other binders but that just holds together a failed casting it is no cure.
Intergranular corrosion of diecast models is commonly known by many descriptive names: Zinc Pest, Metal Fatigue, and Diecast Rot are some. It is a destructive intercrystalline corrosion resulting from the Mazak (Zamak) used to make diecast models being contaminated with other substances. It leads to castings swelling and becoming misshapen. In later stages the castings may craze or develop cracks, ultimately even disintegrating. This was quite common in pre-war toys like early Dinky Toys where lead used elsewhere in the factory got into the mixture but according to Wikipedia this should not happen to items from the 1960s onwards as manufacturing controls should guarantee the purity of the metal.
Impurities in metals used in current manufacturings could be caused by suppliers shipping metal which already contains impurities or contaminants, or it can happen in the plant where the metal for diecasting is melted and mixed and where impurities may be inadvertently introduced. It is impossible for us to determine whether it is poor raw materials or poor manufacturing processes that are the root cause as either end up with the model suffering in the same way. But as I read comments on the Internet that many model makers have suffered from this problem, including PCT Industries, Norev, Corgi and others, it clearly needs to be taken more seriously by people producing the castings.
I had previously heard that Oxford Diecast too had this problem but had never seen direct evidence that this was the case. However, a recent post on the Oxford Diecast Collectors Group on Facebook by Jane Jones shows a destructive case of intergranular corrosion as you can see from her pictures below.
Jane posted: ‘I made a worrying discovery today. I noticed that the rear of this GPO telephones Morris 1000 was bowed, and comparing it to other Morris 1000 vans, it as almost a mm longer. Closer examination showed that the offside was bowing out and beginning to crack . No other model that I have examined seems to have the same issue. Hopefully its an isolated case??‘.
Janes’ photograph is shown below with my added arrows highlighting the extensive areas of distortion.
Jane added: ‘Lookout for the rear distorting. That indicates that the body has elongated because the zinc rot causes microscopic cracks‘.
Sadly Janes’ second photograph shows the inevitable result when the corrosion is as bad as that shown above. Again my arrows have been added to highlight where the ‘bowing’ sections have broken away from the van.
So if you have this Oxford Diecast van it may well be worth checking it. I suspect that this is not an extensive problem for Oxford Diecast collectors or the internet would be full of many more comments. It is a great shame though for those who find their models like this as it inevitably takes several years to come to light and by then the manufacturer is in no position to replace clearly faulty goods.
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