I have an interesting reoccuring problem. Every time I have to do a Mechika, although I use a #10 blade, an ink eraser, and sand paper, and it comes out perfectly white at that moment, the very next day, everything that was erased reappears as a shadowy image of all those letters. I know this has to do with some chemical reaction; I just don't know what to do to avoid this happening other then erasing the first time like I always do and then putting the sta''m aside until the next day and then erasing it again after it reappears, leaving it completely white as I want it. This is very impractical when trying to complete a pair of Tefillin. By the way, the ink I use is Nahari. If anyone has any advice, I'd be very grateful.