I have three vintage pressed botanicals, about 11x14 in size, from around 1900 to frame. I need to overlay the dried flowers with a piece of acid-free non-yellowing acetate to prevent the little petals and other pieces from falling off or leaning against the glass. Looking for a trusted source and a recommended thickness and/or any other pointers. I recall this being talked about in a session at the West Coast Art & Frame show a few years ago, but of course, I can't find those notes now that I need them. Thanks in advance.