Digital BW, The Print

Clayton on the yellowing of Epson Enhanced Matt: "Yes, this is well established.  It is not an 
acid free paper."

While acid in paper is unquestionably detrimental (the paper will eventually fall apart), I am 
not sure it is the only concern. 

I have noticed fairly obvious yellowing --- or at least darkening --- of supposedly acid free 
and buffered "conservation board" from Light Impressions. It started out as a "natural" white, 
and became noticeably more ivory in colour. This occurred not only where light hit it, but 
also where the board was open to the air but not exposed to light in my home (ie, the open 
back of the backing board for a framed photograph hanging on the wall). A few pieces of 
similar board from the same era that were kept in a drawer do not show similar changes. I do 
not live in a high-pollution area, although oil heat probably sneaks a fair bit of something or 
other into my home environment. 

Unfortunately, I'm not sure I can identify any pure rag board from the same era to see 
whether it behaved differently.

Myron