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topic 37680

What can be done to reverse or treat zinc pest?


A discussion started in 2005 but continuing through 2020

2005

Q. I am an antiques dealer, and I run across antiques containing zinc fairly often which are already afflicted with "zinc pest". Usually a dealer will just walk away from such an item, as they are very hard to resell. But is there a treatment to remove zinc pest that leaves the object without ugly discolored spots or splotches?

Chris Mason
antiques - McLean, Virginia


2005

A. Zinc pest? All zinc corrosion products are white or light gray. You can remove them with some chemical solution (5% sulphuric acid, then rinse well in sodium carbonate 5% solution; after that rinse again with water). Any methylene chloride or DMF based paint stripper can be used too. Good luck!

Goran Budija
- Zagreb, Croatia


sidebar 2005

affil. link
"Napoleon's Buttons"
from Abe Books

or

A. Hi, "tin pest" is a little-known issue where the molecules of tin change in cold climates. Something about alpha and beta tin where alpha tin takes up more volume than beta tin and beta-tin is converted to alpha in cold temperatures. I don't know all the technical details. But there appears to be no cure for this condition once started.

Mark Jones
- Toledo, Ohio


2005

thumbs up sign Tin pest is discussed at fair length on letter 740.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


February 21, 2009

A. I believe what the initial questioner is finding is what we in the antique toy business call "metal Fatigue" - the crumbling or cracking of old metal toys. This affects pre-war dinky toys and other toys of that era that are made of ZAMAC (or MAZAC) alloy - this is a zinc tin alloy and if it's been contaminated with lead it will, over the years recrystallize - no cure. Some toys are fine - no contamination - and are worth lots, compared to the distressed ones.

Dave Shelton
- Victoria, BC, Canada


December 13, 2019

A. To Dave Shelton, this is NOT 'fatigue'. Fatigue of metals is due to stress, whether heat, vibration, or directional forces. Bending and vibration will cause micro-cracking and crystalline structures which have no integrity. They eventually cause massive structural failure.

Zinkpest, or 'zinc pest' as we call it in the English-speaking world, is strictly 'chemical' in nature. It is the natural breakdown of incompatible alloys, and it depends on various impurities and alloying mistakes ... or in some cases, purposeful and money-saving reasons during manufacture. Zinc pest is irreversible, and progressive. Those two factors mean the complete loss of the function and of the value of the item in time.

Crandell Overton
- Comox, BC, Canada



Zinc pest and newer diecast models

May 30, 2020

Q. I have quite large collection of model cars. Most of them are quite valuable. I have been reading about the zinc pest problem which affects mainly older diecast material. Is the problem less likely or unlikely to affect later diecast material or should I consider selling my collection.

John Guy M. Moore
- WEST LINN, OREGON, USA


June 15, 2020

To John Guy M. Moore,

The zinc pest problem was for the most part resolved after the 1950s with a few exceptions, but there's been a resurgence of it in replicas made since about the mid 1990s. Certain brands are notorious for it now, while other brands are largely unaffected. Ironically, my experience has been that expensive collector quality replicas seem to be affected by it more often than the cheaper more toy-like replicas. There are particular replicas that have a high incidence of zinc pest; I recently bought an expensive tractor replica, only to find that it was affected by zinc pest. Since then, almost every other example I've seen of that same replica is affected too. And I'm losing an expensive very hard to find tractor replica to zinc pest, as well as a few of my smaller diecast cars. At least a couple of my larger diecast cars are deteriorating and others are beginning to look suspect. I'm keeping most of mine, time will tell what rots and what doesn't. Anything that rots is getting tossed. I am however, very reluctant to buy any expensive new releases for fear of losing them to zinc pest. For more expensive items, I now only buy older releases (15+ years old) that have survived. I don't think there's any need to sell your collection, but be prepared for the possibility of seeing zinc pest in a few items. Contrary to what some people believe, the condition is NOT contagious, it can't spread from one model to another.

Brian Bongert
- Appleton, Wisconsin USA

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