4x5 ground glass holder for Polaroid custom film holders

This is a 105mm wide ground glass holder compatible with the 4x5 back and film holders developed for Polaroid cameras. It has the same film plane offset as the film holders if the ground glass is installed frosted side down. Maximum size for the ground glass is 101mm x 126mm, but it would be best to make it smaller so it will fit without difficulty. It shouldn't be much smaller than 98 x 123mm. Ground glass can be made with silica carbide, water, and another piece of glass, first using 400 grit, then 600 grit.