Re: Superglue +'s and -'s -Reply

["Sally Shelton" <Shelton.Sally@NMNH.SI.EDU>]

The problems associated with white glues (cf. "Elmer's") can't be controlled 
with simple RH, because the stuff is inherently unstable. It will break down 
over a short time no matter what. Good RH control delays this a bit--that's 
all. Anyone who has dealt with old repairs can tell horror stories around the 
campfire for hours. Even in ideal conditions, the stuff yellows, turns brittle 
and exhibits shrinkage withing 20 years or less. (Go read the SPNHC Technical 
Leaflet for more.)

You have to keep a couple of things in mind:
1. Commercial products are *not* made for our particular needs and uses. They 
don't have to be archivally stable for household use, but for specimens and 
collections that cavalier attitude is disastrous. 

2. Manufacturers don't have to tell you everything that's in the soup. There 
can be all sorts of reactive ingredients that aren't, and don't have to be, 
listed on the label. The problem with the white glues in particular is that the 
composition varies so much, not only from manufacturer to manufacturer, but 
also from batch to batch. 

3. Industrial legalese isn't the same thing as normal language. "Inert 
ingredients" aren't *chemically* inert, as you might assume: they refer to the 
fillers and other substances that don't contribute to the reaction the product 
is manufactured for. E.g.: "inert" ingredients in a box of detergent are merely 
the non-detergent ingredients, and they are often very chemically reactive. 
Same for adhesives, consolidants, coatings and gap fillers. They continue to 
react with each other, the specimen and the ambient environment. (Just because 
an adhesive has cured, set or dried DOES NOT mean that the chemical reaction 
has stopped. In fact, it never does.)

4. Similarly, a lifetime guarantee has nothing to do with a human lifetime. A 
lifetime guarantee refers to the average lifetime of the product in laboratory 
testing. Thus, a lifetime guarantee assures you that the product will last as 
long as it lasted in testing and as long as it is supposed to last on average 
based on testing. Very tautological. That time may be measured in months. If 
you assume that a lifetime guarantee means you'll be long gone by the time 
problems arise--guess again. And the manufacturer won't be at fault.

This is why we recommend so strongly that, whenever possible, you buy polymers 
in pure form (e.g. Butvar beads) and mix adhesives/ consolidants yourself in 
small batches to the desired viscosity. And Write It Down (both the polymer and 
the solvent actually used). Someone may very well have to undo what you did in 
the near or distant future.

Cheers,
Sally Shelton
Collections Officer
National Museum of Natural History
Smithsonian Institution