Hi,
I'm an artist considering rolls of Yupo for large-format drawings and have a few questions regarding yellowing and mounting.
 
I happen to have an old pad of Yupo 74lb sheets around and recently used it to do some tests before ordering the large rolls.
I noticed a very slight yellowing, I thought, on the edges of the paper.  It's pretty subtle but it seems to be there, and the pad wasn't in direct sunlight.
 
so my questions are:
 
1) Does Yupo yellow with UV exposure?
 
2) If Yupo is front-mounted with Plexi, the way that photographs often are, does that typically cut down the UV sufficiently to inhibit yellowing?
 
3) Do you know of any reaction that the material might have to silicone, which is used in some front-mounting techniques?
 
4) Given my concern about yellowing, is there a type of Yupo that I should be considering that is different from what I can order through art-supply channels?  
 
many thanks,

Does Yupo yellow with UV exposure? 
** Yes.
 
If Yupo is front-mounted with Plexi, the way that photographs often are, does that typically cut down the UV sufficiently to inhibit yellowing?
**  UV Acrylic (Plexi-glass) filters out 98% of the sun’s harmful UV rays.
 
Do you know of any reaction that the material might have to silicone, which is used in some front-mounting techniques? 
**No, silicones are inert, synthetic compounds with low chemical reactivity.
 
Given my concern about yellowing, is there a type of Yupo that I should be considering that is different from what I can order through art-supply channels?  
**No.  I might recommend coating your final work with a non-yellowing acrylic spray, such as Lascaux Fixativ.  This acrylic fixative is as clear as water, extremely lightfast, resistant to aging and non-matte.  Use it as a final varnish.  Lascaux seals without aging and forms a lightfast, invisible scratchproof seal.

Regarding the yellowing issue. For whatever my opinion is worth; I have been using Yupo for 11 yrs with India Ink. I've had work exposed to normal daylight conditions for years and have seen NO yellowing effects. Go figure!

Use a sealant only when your work is complete, as rework and touch-ups on YUPO become difficult to do after sealing. Acrylic varnishes form a non-yellowing, durable plastic skin that bonds permanently to the artwork. These varnishes cannot be removed, but can be painted over with acrylic paint.

We recommend using a high quality acrylic non-yellowing varnish on YUPO, such as Lascaux Fixativ. Lascaux Fixativ is a transparent, pure, thermoplastic, acrylic resin fixative that has proven successful for many uses, especially for conservation. Lascaux Fixativ is suitable for fixing pencil, charcoal, pastels, wax crayons, watercolors, Indian ink, tempera, photos, lithographs, art prints, rub letters, gold leaf, etc.

I have a stack of Yupo paper between a folder of cardboard lined with acid free tissue. It's been there one year. I am shocked to see there is yellowing (more like pinkish) color change at the edges. I can't figure how this can happen other than by acid from the corrugated cardboard somehow through the acid free tissue. While I can understand yellowing due to UV light, I thought that being inert it would not react so quickly (if true) to the cardboard. I have seen regular paper between cardboard for a year not having this dramatically noticeable an effect. And I don't mean just the pieces on the ends that touched the acid free tissue lined cardboard...some of these were pieces in the middle.

Hi Wendy, there are a lot of variables that come into play with the yellowing you describe. It could be UV contamination in the room where the YUPO is stored. Even though you have a protective cover on the top and bottom of the stack, the UV will still contaminate the edges of the YUPO. And it could also be the cardboard causing the contamination. YUPO is insert but it's very sensitive to UV All papers are, but the yellowing with YUPO just makes it visually more noticeable.

The best protection for any unused paper and YUPO is to place it in an acid-free container, preferably away from any direct sunlight.