Keeping your ink collection organized is a breeze with the Col-o-ring Ink Testing Book! Each book contains 100 sheets of 100 lb/160 gsm European paper, that is acid-free and a bright, natural white. Each 2" x 4" book has a sturdy chipboard cover, is bound with a split-ring so that you can remove, rearrange and reinsert pages as needed. The Col-o-ring paper was rigorously tested to ensure that inks would not feather, bleed or show through. Inks can be tested with fountain pen, glass pen, dip pen, swabs or paintbrush on the front or back of the sheet.