If you are mounting smaller coins (not
sestertii, for example) on a framed backing of cloth or non-acid paper or composition, glue dots ("Zots" for example), available from most hobby/craft stores, are
fine. They are non-acid, as they are designed to mount paper craft items, photos, and so on. I tested them on current American silver
plated coins--no problem. I have been using them for about fifteen years in a frame which opens in front, for
denarii and similar-sized
Romans primarily. but also the
follis types of the fourth century. No slightest signs of ill effects, and the coins continue to tone normally. The glue dots, of the same material which anchors your new credit cards to paper backing in the mail, are inexpensive and come in different sizes and thicknesses, so that the backing dot is invisible. You can use them in a vertical frame, though heavier coins may sag out a
bit over time. My frame sits on an easel with a slight backward tilt, and the coins very rarely sag--if one does, you simply press it back down. If you want to pull a coin out to examine it, you merely rub off the old dot and apply a new one to replace the coin.
Fabric works best as a backing and
comes in a color of your
choice to highlight the coin colors. I
hope this seems a reasonable option. Jim