Lead Oxidation Revisited Again

[Charles Green]

By August 3rd, after my comments on this topic only raised more questions than were answered, I resolved to buy the NRG's back-issue collection which contained a definitive article on the subject -Vol. 43, #1.  I ordered that day but a day after receiving confirmation, the NRG had the integrity to send notice that every disk was discovered to contain a defect and delivery would be delayed until the problem was resolved.  I received the new disk a few days ago.  It was worth the wait.  I'm here to tell you, you can't live without a back-issue collection!  The articles, illustrations, even the old advertising - a disk full of it provides total immersion into ship modeling. 

 

As comprehensive as the article is, I was hoping for more data on wood types most suitable for archival reasons.  As it stands, the article details the problem of acetic acid out-gassing from wood, wood glues and finishes (in general, from any organic material) and its effect on lead.  All wood types, common wood glues and finishes out-gas acetic acid to one degree or another.  A short list of wood types and their out-gassing potential is included.  From that list, red and white oak and basswood are the only woods mentioned that would find common use in modeling and from an out-gassing/archival standpoint, they should be avoided.  From a list of "other material", out-gassing from contact cement and plastic wood is considered harmful.  Shellac seems to be the only finish that does not out-gas acetic acid but it does not block out-gassing vapor from the wood or glue it may cover.  From other sources, I have found hide-glue is considered archival but it is comparatively difficult to use.

 

Compared to open-air display, the potential for damage from out-gassing is amplified many times by enclosing models in exhibit cases which essentially trap and concentrate the fumes.   If made of wood, the cases themselves will contribute to the problem.  Constructing/venting an exhibit case in a way to allow the air within to turn over twice a day is considered adequate for archival purposes.  Maintaining an inert atmosphere within the case or the use of adsorbents was considered impractical. 

 

In spite of the hazard enclosures present, they are considered preferable to open air display.  Dust collecting on a model will attract and hold moisture and destructive micro-organisms, while cleaning the model of dust invites damage as do people too curious to leave hands off.  A type of glazing can be chosen for an exhibit case that will filter UV radiation.  An exhibit case will also protect the model from rapid changes in temperature and humidity.

 

The out-gassed acetic acid effects not only lead but any other material susceptible to acidic degradation.  Rigging is in this category.

 

The article concludes with a bibliography of 30 citations, 15 of which pertain specifically to the out-gassing properties of wood types and finishes.  In the recent past, I have attempted to research another topic by way of inter-library loans.  Lacking bona fide researcher credentials, in this time of shut-downs and skeleton crews, I didn't get very far.  When things open up, I'll investigate pertinent citations from this article's bibliography.       

 

 

 

   

[Bob Cleek]

This research paper from the Curator of Navy Ship Models, Naval Sea Systems Command, is also extremely helpful: https://www.navsea.navy.mil/Home/Warfare-Centers/NSWC-Carderock/Resources/Curator-of-Navy-Ship-Models/Lead-Corrosion-in-Exhibition-Ship-Models/

 

While "lead bloom" or lead oxidation, is the more commonly known issue, it is well for the modeler to become well aware of the archival properties of all materials used in a model and of archival construction practices. "It's a jungle out there!" and there are many materials, or combinations of materials, that aren't really suitable for a model one wishes to last as well as it might. The Navy's curatorial staff has produced an excellent paper, Specifications for Building Exhibition Ship Models, which is the Navy's specifications for any model they commission to be built commercially. While there's always room for innovation, any serious modeler would do well to keep these specifications in mind when building any model, even if they aren't building it for the U.S. Navy.  See: https://www.navsea.navy.mil/Home/Warfare-Centers/NSWC-Carderock/Resources/Curator-of-Navy-Ship-Models/Specifications-for-Building-Exhibition-Ship-Models/

[wefalck]

Weren't these articles on the NRG home-page for a long time ? At least I have been aware of them for some ten+ years.

 

While I have been advocating in principle the conclusions, the problem is, that many of the 'safe' materials and practices are not very useful for the miniature or small-scale shipmodeller, particularly, when building ships from the last quarter of the 19th century on. They are just not practical.

 

One recommendation, however, that is important to heed, is to use as few different materials as possible in any one model.

[Bob Cleek]

59 minutes ago, wefalck said:

Weren't these articles on the NRG home-page for a long time ? At least I have been aware of them for some ten+ years.

 

While I have been advocating in principle the conclusions, the problem is, that many of the 'safe' materials and practices are not very useful for the miniature or small-scale shipmodeller, particularly, when building ships from the last quarter of the 19th century on. They are just not practical.

 

One recommendation, however, that is important to heed, is to use as few different materials as possible in any one model.

I wouldn't be surprised if they were on the home-page. They are "classics." I believe I posted the URLs here once before. I agree that miniature and small-scale models do demand certain accommodations. The Navy standards aren't specifically intended for miniatures, but rather for models intended for museum display. Avoiding dissimilar materials is always a good practice. I'd add to that avoiding modern materials with unproven archival qualities. Many may not value their models enough to take such pains, but they may be selling themselves short. We never know if long after we're gone, our work, if it survives, may have value we never imagined. The builders of the "Prisoner of War" models come to mind. I'm sure they never could have imagined the present value of their few works which have survived. They used natural materials out of necessity and these were "archival" by chance. Were they built with many modern materials commonly used today, particularly the products of modern chemical technology, I doubt they'd have lasted as long. I experienced this phenomenon personally just the other day when my 1970's vintage Singer sewing machine "packed it in" when it's plastic gears crumbled to bits and pieces. (Fortunately, parts are available for me to rebuild it, although if one were to have a repair shop do so, it would be cheaper to buy a new machine.)

[mtaylor]

They redid the NRG page so they may have moved the links, etc.

[kurtvd19]

3 hours ago, wefalck said:

Weren't these articles on the NRG home-page for a long time ? At least I have been aware of them for some ten+ years.

Yes it was there and still is.  It can be read off the NRG website or downloaded as a PDF.  The link is below:

https://thenrg.org/resource/articles/materials-in-ship-models

[wefalck]

Thanks to the 2nd Law of Thermodynamics, everything will crumble away eventually ... just a question of time.

 

Not all modern materials are bad and deteriorate quickly - otherwise we wouldn't need to worry about plastics in the environment. The problem are plastics that contain plasticisers. They gas out with time and the remaining material becomes brittle. There is also the problem of UV-exposure that can brake bonds and cross-links in plastics, leading to their degradation.

 

Certain quality plastics on the other hand are very stable, such as phenolic resins ('bakelite') and methacrylates ('Plexiglas'). We have bakelite artefacts that are well over a hundred years old by now and that are as good as new. Plexiglas has been around only since the 1930s, but we have still a lot of unaltered artefacts from WW2 and before.

 

Often it is not the material itself that is a problem, but their combinations. We generally credit the artisans and artists of old to have been better in choices, but this is not always true - keeps the art restorers and conservators busy. Think of silk for sails and threads, certain dyes and inks (e.g. iron gallus ink) that corrode the paper, etc. Virtually all natural organic materials are biodegradable ... A big problem are post-1960s artworks, when 'artists' began to experiment with new materials and techniques and combinations thereof. Such works can be a real headache for the conservators - from the aesthetic point of view perhaps they shouldn't worry too much

 

 

[druxey]

Well summarized, wefalck!