Digital BW, The Print

I was just having a heck of a time trying to get two prints to match 
tone. (Ut2 on a 1280). One is velvet fine art, and the other photo rag. 
I made about 6 prints trying the get the photo rag not to warmer than 
the velvet.....then I figured out that the velvet print was in a frame 
under glass. I was using identical matt boards, and I had the matt 
laying over the the PR print. The velvet print was 12x15, and the PH.R 
print was 8x10. Finally figured it out when I laid the smaller print on 
top of the larger mounted print and saw that the glass had totally 
changed the color of the matt board. The print under glass looked 
better. (The reason one had glass and the other did not was because I 
broke it.....).....so anyway, I never hear much about the effect of 
glass on the color of a print. this is cheap glass from michaels, so 
maybe that is an issue also.......DM