[NHCOLL-L:2223] Re: Fw: Storage

[Jim Druzik]

To Dr. Fourie's question about wood versus archival materials boxes, permit me to expand on this topic, since my lab's been working on this and similar themes for a number of years. Indeed, natural wood products, particularly hardwoods, and wood by-products, including but not limited to all uses of mechanical pulps, do produce acetic and formic acids which will jeopordize acid-sensitive materials. However, this alone is a very simple model for risk assessments in storage. In fact it avoids considering most of the parameters cotributing to the larger picture. .Above and beyond these two simple organic acids, woods will produce other break-down products that also can diffuse to other vulnerable surfaces. While the decomposition of weaker lignin bonds are mostly driven by photo-oxidative processes, the thermal degradation of lignin is not a zero risk in darkness. These are acidic AND highly colored products and are responsible for a great deal of brown discoloration on  identification labels and other cellulosics. So you have sources of discoloration and staining as well as classic risks from acid hydrolysis. Yet, the problems you fear are equally ones caused by local concentrations rising significantly above ambient levels, and this is where massive damage has been found in encapsulations, closed display cases, and wood-containing closed storage boxes. While the extent that ventilation, with or without chemical filtration, would mitigate wood effects over a distances of a few centimeters to several dozen centimeters can be estimated, the propoderance of evidence suggests that such enterior ventilation is never efficient enough nor are adsorbents. If you have an acid-sensitive or lignin-stainable material in a sealed wood box, it is only a matter of time before the effects show up. If the wood boxes are open, you have no way of knowing efficacy because the bad effects (certainly not the benefits) may not be visible in a short time. Acid damage to cellulosics is a difficult reaction to monitor in a lab simply because the effects are demonstrated far greater through a change in physical performance than having effects that are visible. Are you sure it's not the same for some fossils? Archival boxes, open or closed, on wooden shelves may be safer due to diffusion and passive ventilation but this may only slow down the inevitable. You should probably look at storage wth the ideal of asking why the storage materials can't be as stable as possible.   

James Druzik
Senior Scientist
The Getty Conservation Institute
Getty Center
Los Angeles, California

>>> "Dr H. Fourie" <hfourie at nfi.co.za> 02/26/04 05:06AM >>>

----- Original Message ----- 
From: Dr H. Fourie 
To: NHCOLL-L at lists.yale.edu 
Sent: Wednesday, February 25, 2004 10:08 AM
Subject: Storage


Wood versus archival material boxes:
A year ago I went through a lengthy exercise to replace painted wooden boxes in our fossil type room with polypropylene containers.  To provide support and stability I used polyethylene foam sheets inside the containers.  One of the products I used is called Correx (a plastic corrugated box).  No lids are necessary as these are stored on glass shelves in closable cupboards.  Now these containers are going to be replaced with wood.  I was under the impression that even natural wood emits gases such as acetic and formic acids detrimental to Glyptal covered specimens.
My question: Is this a good idea.  Never mind the additional R 8000-00 they intend to spend.

Dr H. Fourie
Research: Vertebrate Palaeontology,
Transvaal Museum, Pretoria
South Africa