Thought I'd share this with you all. It came in as a question from a reader at Toy Cars and Models, and after doing the research, I thought it might be of some interest. I feel sorry for the guy - and I've seen this problem first hand.

Dear Editor:
I have been collecting die-cast cars for several years, but now I may stop collecting them. I have two 1964-1/2 Mustang convertibles made by Revell, one of which is the Indy 500 Pace Car. The other one is identical to the one that is pictured on page 50 of TC&M's August 2003 issue. The print says, "Revell's older 1964-1/2 Mustangs are worth seeking out in convertible or coupe form. Look for several 1960s colors, too." My suggestion is not to buy any of them.

I bought mine new and kept the cars in their boxes because I wanted them to remain in new-looking, unplayed-with condition. A passing glance at the red convertible revealed something odd. I took the car out of the box to look closer at it. It looked like it was melting. All corners of the hood were curling up, the hood had cracked in half, stress cracks appeared everywhere. I tilted the base the car was mounted on, and both doors fell off. The paint is crazing and bubbled. The car is broken everywhere because the casting is so brittle. I immediately took the pace car convertible out of its box to check it out, but it appears to be OK. I can only wonder if it will soon fall apart, too, since it is from the same casting as the other one.

I thought these cars were supposed to last - that's why I bought them. I feel Revell should make good on these cars and give a refund to anyone that bought them, even if they are old. I can't afford to replace them if this keeps happening. Right now I'm not working.

Please tell everyone to pass on these cars.
XXXXXX XXXXXX
Capay, Calif.

Hello, XXXXXX –

Thanks for writing.
First, the good news: you needn’t worry too much about the untimely demise of that Revell Pace Car. Unless the two models came from the exact same batch of metal (not just the same mold set), you’re probably cool. Now, the bad: the problem happens to cars from virtually every maker, and attacks with almost no warning. Even worse, once it starts, you can’t do a thing to stop it.

Your old Revell model fell victim to an extreme case of “intergranular corrosion”, a phenomenon that occurs in castings made from ZAMAK – the stuff diecast cars are made from. ZAMAK is a hypoeutectic alloy of zinc and approximately four percent aluminum (more aluminum than that, and the alloy is called “hypereutectic” – and loses its ZAMAK name), as well as a few trace metals. Those trace metals can be part of the problem – but more on that in a minute.

ZAMAK’s been around since the early 1900s – some say as early as 1896. The reason it became such a popular material is that it’s tough, relatively inexpensive, and it can be cast into very detailed shapes. That’s made it the material of choice for industrial applications – as well as metal toys – pretty much from the beginning.

I was moved by your story, and it’s one I’ve heard from several collectors over the years, so I decided to do a little light reading on the topic. What I found was:

1) There is no such thing as “light reading” when you’re discussing metallurgy; and,
2) The problem is so prevalent that there are actually scientific papers published on it.

Yes, it’s true. So I refer you to document NLR-TP-2005-205, “Corrosion-Induced Cracking of Model Train Zinc-aluminum Castings” (R.J.H. Wanhill and T. Hattenberg, National Aerospace Laboratory NLR, May 2005), probably the most comprehensive study yet undertaken in an effort to explain what happens to our prides and joys when the lights are out and nobody’s home. After reading the paper (which almost caused “intergranular corrosion” within the wrinkles of my brain), I learned that the presence of lead (Pb), cadmium (Cd), or tin (Sn), in amounts that exceed approximately .005 percent by weight, will pretty much send a diecast train – or your model car – to the dustbin without so much as a how do you do.

The rate at which this does or doesn’t happen depends on the level of metal contamination – and moisture. And heat, since you’re asking. Warm, damp places will accelerate the evil deeds done by those filthy metallic stowaways, which get into the dendrites (crystals formed within the alloy as it cools) and start a reaction that causes the metal to literally come apart at its molecular seams. This is why I never store my models in my mouth. Though I’ve been told they’d probably fit.

Brauer & Pierce examined the phenomenon in 1923, and I’ve had firsthand experience with it on a pair of Ertl/Supercar Collectibles COPO Camaros on which the doors abruptly turned to dust – after years of what was considered “safe” storage in their boxes.

While there’s no way of predicting which models will self-destruct, there is something you can do to help prevent the zinc termites from chowing down on your collection – wax it. It’s been shown that the models usually deteriorate from the outside in, so keeping a good polish on hand and giving the cars a once over every now and then might be a good idea. Yes, that means taking the cars out of their boxes. But if you keep all the original accouterments that came along with the model, you can still get top buck when you want to sell or give the car away. And, you might even actually get to enjoy the thing. Just my opinion.

So, you see, it’s not a Revell problem. Revell makes some great stuff – just ask my credit card. So, if and when you can do it, you might pick up another of those little ragtops. But, as with any model of any vintage, I’d advise you look for telltale signs of bubbling or large pits in the paint before you plunk cash on the barrel.
Good luck – and happy collecting.