No, the ink is quite transparent and lets quite a lot of light through. That's how you can use it on overhead projectors. If you make any of these custom screens do make sure you use OHP Film For Inkjet Printers. This is very important (if you're using an inkjet printer that is) as the ink will not dry if you use OHP film for laser printers or dye-subs etc. and it would smear all over the place. Of course if you're not using an inkjet then use the correct film for whatever printer you are using. I haven't tried making screens on any other type of printer so I can't vouch for it's effectiveness. If anyone tries it on a colour laser or dye-sub printer etc. please let us know how it turns out.