Styrofoam ? These things came in cardboard boxes . Styrofoam was not used by Marklin for another 20 or so years. But, thanks for the help. I have a Dremel cordless and will start with a brush to take off the oxididation.

Anyone else have thoughts or solutions ?

Dave

What is going on is not zinc rot, but a phenomenon that's known as tin pest. The cause is a wrong mixture of the alloy. Under certain circumstanes this causes a change in crystalline structure of the tin. One of the circumstances is low temperature, so one measure to prevent this problem, or at least to slow it down, is to keep your models at room temperature.
Search on google for tin pest and you will find lots of sites that deal with this problem.

Interesting reading.. Looks like the highest priority is to get rid of the crystalised material as it acts as a catalyst for further corrosion... See http://www.finishing.com/188/49.html

Scary stuff...

Well, this is what I saw in a cable documentary (I believe in the Odissey channel) where a die cast car collector was explaining this styrofoam related problem.

Anyway, in the 3097 BR23 restoration I finished a few days ago, of which I posted a picture in the Collector's Corner topic, I did what I explained above to remove the crystalized deposits.

To remove the larger deposits, I used a brass wire rotary brush. Then I went to manual removal with an old X-Acto blade and sandpaper. Then I picked up the Dremel again with felt rotary polishing tool.

Then I airbrushed it with dilluted Gunze Sangyo Surfacer grade 1000 and brush-used some grade 500 in places to fill in the roughness. Then I sanded it all flat (the main affected area was the top of the cab and some of the boiler top) and painted with Revell no7 gloss black enamel.

Let it cure for 3 days and applied a 30/70 mix of Xtracolor gloss varnish/Modelmaster flatcote. I obtained a nice satin sheen that looks like the original.

Only time will tell if the pest will surface again or not.

I went through the finishing.com link mentioned above and think that the problem therein mentioned is that of unpainted tin plates and other tin collector/antique items.

I believe the roting lok problem may be alleviated through the use of thicker coats of paint than Märklin used. From what I've seen in old loks, the paint job looks like a very thin coat of cellulose based paint. This wears out over the years and exposes the alloy to air.

I think that a thicker coat of paint may help a great deal in stopping the phaenomenon. I read somewhere that today's loks are painted with resin based paints and the painting process even involves oven baking, but I haven't seen any confirmation of this. Being true, this should be a very resistant coat.

Luis

No, I don't think so. Tin pest affects things made of tin (and sometimes alloys containing a large portion of tin, like solder). Tin pest is caused by low temperature, since the stable crystalline structure of tin is different below 18 C than above 18 C. For tin alloys like e.g. solder the critical temperature is much lower (below 0 C).

The Märklin locos are made of zink alloy, with no or very little tin. One of the causes is a wrong mixture of the alloy, as Nico says, but it still isn't tin pest and the temperature is probably less important.

Doomed - does not sound good.. [:(] Still it seems better to scrub it out (with the brass one) and seal with the clear varnish as Luis says in his posting.. Gasp - such a small thing . Imagine if we had these problems with real bridges...

Yes, in Klaus Eckert's "Das grosse Handbuch MÄRKLIN HO" there's one full chapter about it ... "Nope", he writes, "once it's inside that shell is rotting away" [xx(]

John

The cause of the zink pest / tin pest is accurately described by Guus. Luis's recommendations earlier are EXACTLY the right steps to take to atleast improve the appearance. I have done this several times on - particularly - old 809 metal coal tenders (ie G800, F800, GN800) with excellent results, i.e. no more evidence of corrosion.

Peter Neumann
Florida

Hi all,

I agree with you Per the name of the problem is Zinc Pest or Zinc Rot if you like.The way I understand it ,is that the material used in manufacturing the locomotives is called Zamac,which is an alloy of mainly Zn (zinc) and in addition Al (aluminium) Cu (copper) and Mg (magnesium).Inevitable there will be some other elements like Fe (iron) Pb (lead)and here she comes Sn (tin),which are seen as contaminants and their share must be kept as low as possible.
Might be that the latter gives some confusion in naming this phenomenon.
It's a long time ago I had training in Mechanical Engineering and I must stress that I only express my vision in this topic and it's in no way academically verified to be correct.

Just kidding : Märklin has found the definite solution of keeping locomotives in top condition forever.You all know her: A platinum crococodile with ruby eyes made in 2000.

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originally posted by John:

Yes, in Klaus Eckert's "Das grosse Handbuch MÄRKLIN HO" there's one full chapter about it ...
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Thanks John for recommending this book in another topic.it's a gem .

Best Regards
Guus

George, thanks for that scientific point of view - now even I can see the "chemical picture"
Regarding value I guess there's nothing lost when painting a rotten and "restorated" loco. Since it's pested, anyway - all substantial collector value is already down the river ...

Best Regards
John

Try the brass brush as I suggested earlier.

Luis