REFILLING PROCEDURE:A color HP ink cartridge is a plastic shell with 3 cells/chambers having a piece of sponge in each cell. There is a sticker on top of the cartridge. When you remove that sticker, you can see small holes and through those holes you can see three differently colored pieces of sponge. Note the color of the ink on the sponge in each cell. Refill the cartridge with the respective color of each cell. Take few ml Yellow ink in a syringe, insert the needle through the hole so as to just touch the sponge for yellow ink and inject as much ink as the sponge can absorb. Repeat the same procedure for Magenta and Cyan also. Use separate syringe for each color. After refilling, fix the sticker back. Now your cartridge is ready to use. The refilling procedure for black cartridge is also similar. Do not touch the copper PCB & head/nozzle of the cartridge while refilling. Take special care for not to mix ink in one cell into another cell.After refilling, If ink leaks through the nozzle, keep the cartridge on a tissue paper/news paper, so that the nozzle of the cartridge touches the paper. The excess ink in the cartridge will be absorbed by the paper. Keep the cartridge in the same position till there is no more leakage. If there is no leakage, then you can put the cartridge in the printer, run the head cleaning utility and then start printing.There are you tube videosof our own product in the following links, you may watch that for detailed instructions, color: https://www.youtube.com/watch?v=MtU6sB2zvtI&t=16sblack: https://www.youtube.com/watch?v=ySdi1w9ZmgA&t=1s.It is better to refill a cartridge while some ink remains in it.