How many of you out there are still wrapping this class of objects with glassine then virginpoly? Is this an outdated technique? Have most of you moved on to using just the virgin poly? Any thoughts either way as which method is more "correct" or is safer for the art? Just want to see what the general consensus was out there on this method, as I'm considering changing from glassine+poly to poly only.
You will probably get faster and more numerous responses to this question by submitting it to the paccin list serve ( http://www.paccin.org/content.php?110-ListServe ) but just to start off the conversation here I would say that most museums that I am aware of and most reputable art service providers I have dealt with have dropped the practice of using Glassine as a primary wrapping material for framed paintings.
The basic reason as I understand it is that it doesn't really do much of anything. At one point I think it created a barrier between the frame and slip agents and plasticizers found in Poly with a high proportion of recycled polyethylene (like some films commonly found in home improvement centers). The use of high quality virgin poly eliminates this need. The other reason sometime cited is that glassine, as a paper product, is hygroscopic (absorbs moisture) that could result from condensation. The flaw in this reasoning is that the hygroscopic capacity of a thin layer of paper - when compared to the relatively small volume of contained air - is miniscule when compared with the buffering potential of the mass represented by the painting itself (wooden frame, wooden stretcher, canvas etc...). The physics of this issue only begins to become a concern if the object in question has been maintained at a relatively high humidity level (65% or higher) and is going to be exposed a significant drop in temperature during transit. In other words paintings maintained under what we tend to consider Museum conditions and wrapped in virgin poly have no need of glassine - it least that is what I have been told.
Plus it should be noted that glassine when creased becomes abrasive which can damage gilt frames when re used. So back when it was commonly specified that glassine should be used as a primary wrap it was also commonly specified that new glassine be utilized at each venue.
I would be curious to hear any reasons folks are giving these days for this practice to be continued or revived. Mostly what I have heard whenever I have been able to ask is just "this is how it is done". As someone who has wrapped hundreds and hundreds of framed objects this way I don't have anything horrible to say about it. It is the kind of thing that is easy to do.... just by force of habit. But if questioned, I also just can't really justify the added time, cost or waste of material.