If anyone out there is considering building an IR-related project and is looking for something to block visible light but pass IR, consider the wrappers from M&S Cherry Liqueur Chocolates !
Each wrapper is about 10cm square. Eight layers were found to be enough to drastically attenuate visible light while having no noticeable effect on the IR from a TV remote. The only side-effect of creating a filter this way is a slight increase in the dimensions of your waistline.