Apple is using a bonding agent called Organofunctional Silane Z-6011 to bond the layers of glass. Apparently, Apple (or more likely Foxconn) is shipping these products so quickly that the evaporation process is not complete. However, after one or two days of use, especially with the screen on, will complete the evaporation process and the yellow “blotches” will disappear.
How do I know? I was involved in pitching Z-6011 to Apple.
If this is to be believed it is good that the yellowish discoloration will go away after some time. But what the heck is Organofunctional Silane Z-6011? After googling a bit I found that it is also called Dow Corning Z-6011 Silane. It is a coupling agent used to improve adhesion of plastics, resins and elastomers to inorganic materials and surfaces (full production information can be found here in PDF). Here’s some info on drying it:
After applying this silane, the glass or mineral surface can be air-dried or dried briefly at 105 to 121Â°C (220 to 250Â°F) to effect complete condensation of silanol groups at the surface and to remove water and/or traces of ethanol from hydrolysis. Optimum application and drying conditions, such as time and temperature, should be determined for each application before use in a commercial process.
I guess Foxconn misplaced the note about optimum drying conditions. By the way, when Dow Corning Z-6011 Silane is exposed to moisture it generates ethanol. That didn’t sound good so I looked up potential health hazards of ethanol. There’s a lot. It is suspected of being a carcinogen, cardiovascular or blood toxicant, developmental toxicant, endocrine toxicant, gastrointestinal or liver toxicant, neurotoxicant, reproductive toxicant, respiratory toxicant, and skin or sense organ toxicant. For more info check out Scorecard.org.