I do not have a single precise answer, but doubt there is any way to 
reverse this. The problems are not simply related to the effects of 
light, and may also relate to coexistent heat, moisture and various 
chemical constituents. Here is one general discussion from 2005: 
http://www.pbs.org/wgbh/nova/charters/fading.html . Here is a NEDCC 
leaflet that has some general discussion: 
https://www.nedcc.org/free-resources/preservation-leaflets/2.-the-environment/2.1-temperature,-relative-humidity,-light,-and-air-quality-basic-guidelines-for-preservation 
.

Here is an older discussion of hypotheticals: 
http://www.cool.conservation-us.org/byorg/abbey/ap/ap07/ap07-1/ap07-104.html 
. The Getty has published a couple of related books on the subject: 
http://www.getty.edu/conservation/publications_resources/books/historical_cons_paper.html 
.

Perhaps someone with more direct experience in these sorts of 
conservation efforts can make comments?

      Joel Kovarsky


On 5/22/16 12:22 AM, Michael Holt wrote:
> I have encountered some reproductions of maps from the early 1600s.   
> They're on that fake parchment that is also used on the reproductions 
> of the Declaration of Independence (also on the same wall).  What is 
> it that causes those documents to turn dark with exposure to the sun?  
> Is there some way to remove it?
>
>
>
>
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