I set the microwave at maximal power and the whole sponge became a smokey mound of greyish ashes
You had to go and spoil a good story..I would think that microwaving the cartridge would ruin the chip.
No…4 - Is it absolutely necessary to get the cart weight down to around 13 grams as advised by Jose Rodriguez and others?
Yes, of course. In my case, it were BCI3/BCI6 chipless cartridges from the first generation of PixmasI have also found that changing the paper a couple of times speeds up the drying. It still takes some hours though.
I would think that microwaving the cartridge would ruin the chip.