Will pewer decay/rot ?

[Tyreal_human_fighter]

I have heard of lead rotting and I was just wondering if pewter does the same ?

 

 

thanks

ty

[Joe Kutz]

All things will. Even metals like gold and silver to some extent.

 

The lead rot or bloom that was a somewhat common plague to higher lead content miniatures - however the pewter alloy tends to be more stable than the lead (which is really already quite stable). Tarnish is more common and generally is harmless and shows by a slight yellow or dark brown/black tinge to the metal.

 

In terms of the more feared lead rot - I have never actually had it happen with a mini I have owned. I have seen others, and I have had it happen with various lead parts over the years - but it isn't something which is really a huge concern. Normally it gets caused by acetic acid from finger tips transferred to the miniature or part - though it can come from other sources as well (PVA glue will cause bloom rather quickly on unprotected lead). Worse still, certain paints can actually cause bloom and the protective coating that you thought you were applying can cause the miniature to crumble.

 

Anywho - yes it can happen. In most cases though, you don't have to worry too much.

[Doug Sundseth]

For more than you probably want to know about lead rot, see Lead Corrosion in Exhibition Ship Models. Note that wooden display cases and many common chemicals can exacerbate the problem.

 

This is specifically a problem with lead miniatures, though. Lead-free white metals have much less problem with corrosion than high-lead alloys. So it's probably not a problem unless you have fantasy miniatures produced before the mid-90s. (I'm pretty sure that many historical miniatures makers took longer to go to lead-free alloys, though.)

[skya]

Another good link about how to deal with lead rot from Gearge R. R. Martin's Website.

[GreyHorde]

With all due respect, I disagree. IMHO, Mr. Martin's article is, in a word, terrible. It seems to me (YMMV) that he never actually read the naval ship model museum curator's article he also linked to. Instead, he quotes Bert Caldwell without understanding the science. He tosses around anecdotal evidence interspersed with fuzzy logic and a recipe for an 'elixir', in itself and the application of which read like a voodoo ritual.

 

I would skip Mr. Martin's article, carefully read the naval museum curator's, and hopefully take away three simple things:

1. Lead carbonate -- the whitish, powdery substance often referred to 'bloom', is not rot or rust. It is not oxidation. It is not a disease. It is a chemical reaction, a form of corrosion, that requires lead to be in contact with acid (usually acetic) and carbon dioxide to act as a catalyst.
   
2. Remove any part of the equation and the reaction cannot start. No lead in the piece = no reaction. No acid in contact with the lead = no reaction. Not enough carbon dioxide to start (catalyze) the reaction because fresh air is circulating, even slowly = you guessed it, still no reaction.
   
3. If all three required ingredients are present in sufficient quantities, in the right environment, and the reaction does start, it can be stopped. It is not contagious or airborn like a disease or pathogen. Remember point number 1 above? It is a reaction and as such, it can be stopped. The damage is done, the part can be repaired or replaced, but the reaction can be stopped by removing the lead carbonate which would otherwise continue to produce acetic acid. Cleaning without snake oil or animal sacrifice under a full moon is one way to remove part of the reaction. To prevent recurrence, if you remove part of the process, the reaction cannot start (or restart).
   

[skya]

*falls over laughing*

 

Intelligent, scientific, and amusing response noted and appreciated.

[Joe Kutz]

Keep in mind that the Navy article only deals with one form of lead rot - and it isn't terribly scientific either. In addition to the lead carbonate that they discus, you have a few dozen other possible compounds which you might come across which have different sources. Some of them are hinted at but not explained in their article (lead oxide for example is often caused by UVA light, and leads to a golden yellow tinge). There are also several paths to the same end. The lead acetate can form with immersion in several of the environmentally friendly strippers (Citristrip is one if I recall correctly). It normally manifests as light white dust on the surface - etching the metal underneath it.

 

With alloys you also get into problems related to the other metals involved. Remember everything will corrode to some degree; and if the tin, antimony or bismuth used in the low lead pewter blends used today - you will see a different symptom with different causes and different solutions.

 

Also, don't think new minis are safe. The vast majority of miniatures still contain lead to varying degrees. Most are around 10% lead, though that can vary a lot from manufacturer to manufacturer.

[GreyHorde]

@Skya - cool! It's good to hear read you laugh!

 

@Joe - yep, you make good points about additional sources and other kinds of damage. I won't debate a comparison of the degree of scientific evidence, except to say while the naval article is narrow in focus and a bit light in some areas, it beats the crud out of Mr. Martin quoting Mr. Caldwell with "Lead Rot is lead rusting, and its primary cause is moisture in combination with lack of air circulation." That is just so wrong, in several ways. The only part that comes close is the lack of air circulation.

 

My guess with Citristrip and other environmentally friendly agents would be that it's still an acid + carbon dioxide = lead carbonate reaction. 'Natural' cleaners and strippers may include citric acid (fruit-based), acetic acid (typically vinegar-based, again from fruit/fermentation), or some other mild acid. That's probably enough to account for the formation of lead carbonate, the white powdery substance that etches the surface. You may be right, it may be lead acetate and have basically the same effect. That's just my guess, though, and I have no good way to test or prove it out. After all, I'm as anecdotal and unscientific as the next guy.

 

The one and only case of true lead rot I've had in 25+ years of collecting was on a few late 70's - almost 100% lead - minis stored for years in a friend's musty old basement. They were left in their cheap cardboard (high acid & carbon dioxide content) boxes, in cheap foam (high acid content) trays. The boxes, trays and minis were all disintegrating due to the acids and lack of any air circulation to clear things out. On the other hand, I've had pure lead in bulk and hundreds of high-lead content minis -- a lot of them home cast -- stored in all kinds of containers and locations without any problems at all. So, generally, it's not something I worry about. It just doesn't happen on its own, it takes a combination of things to cause any damage to a range of nearly inert metals.

[Joe Kutz]

Yeah, I agree it isn't something that you need to worry too much about (as I said in my first post). I have never actually had it happen with my miniatures - but I have had it happen with a number of other things (radiators, coolant couplers, plumbing joints and on a near yearly basis with a dozen or so soldered fittings in my shop air system).

 

The lead acetate and lead oxide are actually precursors to the lead carbonate. If you read the description of the rot process in the naval article, you will see them describe a series of changes leading up to the bloom occurring. Starting with a discoloration (lead oxide), followed by a light powder (lead acetate) and finally the bloom (lead carbonate). It doesn't happen all in one step, and the process needs to follow a specific series of changes to get to the next step. In the case of lead oxide - oxygen, lead and UV-A light. Nearly impossible to eliminate any of those from the formula. To go to lead acetate you need lead oxide and acetic acid. The acid is the easiest thing to control - though other acids will lead to different compounds (and those lead to different compounds as well). Uric acid from sweat on fingers will lead to a light grey hard crystal (forget the name of the compound though).

 

In the case of the "safe" strippers, the resultant reaction looked as though it stopped at the point of lower lead salts like lead acetate. This can be removed fairly easily, and normally leaves the metal looking like a wire brush was taken to it. I wasn't able to inspect the actual miniatures though, and I haven't had a chance to do any of my own tests - but the miniature was a fairly recent GW miniature. I don't recall the stripper used...but I keep thinking Citristrip. Once I get a chance to dig through the pictures I have saved I plan on putting together an article that covers the various forms of corrosion specifically related to miniatures as well as the sources and precautionary measures which can be taken in order to avoid it.

[Joe Kutz]

Hate topics like this...makes me crack open the engineering books...

 

Anywho, after a bit more research into the other metals used in popular pewter alloys - I've come across a few interesting things (interesting to me at least) which go to explain why the lead rot is still present in low lead alloys (even 0% lead silver solder which is approved for use with potable water).

 

Antimony follows an identical salt path as lead. Antimony Trioxide, followed by Antimony Acetate. They manifest as a white powder - however they do not progress to the full on bloom seen in lead carbonate.

 

Bismuth also can lead to a buttery colored bloom (as opposed to the normal white bloom seen with lead and antimony).

 

Tin will bloom with normal exposure to air into Tin Oxide (black) or Tin Dioxide (white) and in the right air conditions you will also see it form Tin Chloride or Tin Iodide (both from airborne pollutants). Although the tin processes are normally catalyzed by heat, it can happen as well due to electron excitation caused by light (the UV-A which leads to lead oxide as well).

[Doug Sundseth]

One of the problems with the lead-carbonate sequence is that the corrosion products are gas permeable. In this, they are like iron oxide (rust). Once the process begins, it will continue unless you change the conditions and stop the corrosion.

 

Some other metals have much more benign corrosion paths. Aluminum is quite reactive in atmosphere, but the oxide is not gas permeable in normal circumstances. The result is that the surface oxidizes, but then the process stops. Similar things happen with copper alloys (patina formation), which stops when the bare metal is covered.

 

While any metal can corrode, experience has shown that other metals commonly used for figures are much less likely to have significant corrosion problems. And, of course, lead is unlikely to start to rot. When it does start, though, immediate action is necessary.

 

Finally, most miniatures companies have been using lead-free alloys since the mid-90s, though I was surprised to find that Foundry and Rackham say that they use lead in their white metal.