Thank you all so, so much for your wonderful contributions and fantastic images!
Ed, I think the cardboard on the backs of the dozens of used up notepads would be perfect! Thanks for the suggestion.
I tore the house apart, before I saw Eds post, and found some really old, cheap matte and used that for the time being.
Getting the focus right on this was very difficult. As well as getting the exposure right. In the GG, the image looks very dark so I assumed I'd need a longer exposure time. Not so. The standard Holga shutter speed worked fine. Problem was the focus. I couldnt get it to focus properly until I decided to mount the lensboard on the inner lip of the mouth of the bellows. Now I can focus selectively, just a little, as well as use some tilt. I have to use the special lens attachment that came with the Polaroid back for the holgaroid set up to get it to focus at all though. I forget now what that is called, even though I knew the name of it all day long. Aging really is a pain.
Anyway, here is my frankincamera.
Diopter!!! Thats what that extra lens is called. LOL!