I've always used Rising White Museum Board to mount an over-mat my black and white photographs. I mount photographs on 2-ply and over-mat with 4-ply.

But, to save expenses, I'm wondering about using Crescent, buffered, matte board to over-mat my prints. I would still dry mount prints on 2-ply Rising White. When I mount a print for framing, I only sandwich the over-mat with the print itself. I don't tape the over-mat board to the 2-ply museum board on which the print is dry-mounted. Nor does the over-mat directly touch the print itself.

To my question, is this acceptable? Will there be any risk of contamination? In particular, I'm considering using Crescent Board 9502.