Ctein and others have identified particular problems with RC papers, possibly caused by the Titanium Dioxide that is used to whiten the paper acting as a photocatalyst when exposed to light If I remember correctly, Ctein wrote about it in his Post Exposure which is available as a free download from ctein.com. Unfortunately I don't have my copy handy to confirm this. Wilhelm Research states that even at low illumination levels with UV-filtered light, B&W RC prints may be subject to light-induced oxidation of the silver image (http://www.wilhelm-research.com/pdf/..._HiRes_v1a.pdf p. 578)