Graph paper used by Chana Horwitz

Chana Horwitz seems to have frequently used Keuffel & Esser Co. 8 × 8 to the inch graph paper. There were a few pieces in the Raven Row exhibition on 10 × 15 inch sheets with an orange grid. It looks like K&E was acquired in ‘87, wonder if she stockpiled a bunch of it. Also, food for thought: how do you mount+frame mylar in such a pristine way without any show-through?