Heidi, I was going to mention and forgot, that I have to try out a few of my vellums…but they were from different companies. The first was from Martha Stewart vellum ROLL--I am not sure how she meant for this to be used but it was the first vellum I ever saw/bought and I bought it probably 6 years ago at least and I use it once in a while---it's a pain to use b/c after you cut off a piece off the roll, it will roll up since that was how it was stored. I have to heat it and un roll it and lay between books. :ticked off:
Anyways, when I started doing this technique with MS vellum, it would crack always! and so I went and got out a Recollections vellum piece I have and it was fine---well you could still crack it if you really press but it was pretty good with the pressure. The last was a thick vellum sheet (large too--poster board size) I bought from Hobby Lobby on clearance in the drafting section (I didn't' know they had vellum in the drafting section) and it too will take the pressure.
SO I am not sure if vellum can go "bad" or not or if it is just the quality of the vellum from the Martha Stewart roll----good thing I only paid $0.01 for it!!---seriously it was a penny! When things have been clearances for a LONG time at Michaels, things will go to a penny (or they used too) and they are suppose to take them off the shelf and donate, but once in a while you find a penny item and according to something I read, they are suppose to sale it to you. NOw with my Martha Stewart roll the girl didn't care and thought it was cool I was paying only a penny.
It was the first time I ever saw a penny clearance at Michaels.