An empty ribbon of the 9-pin printer Commodore MPS 1550 C (which is mechanically identical with the Olivetti DM 105) can easily be refilled using stamp pad ink. Here is how:
First make sure that you have a working ribbon cartridge. If you turn the knob clockwise, the ribbon should move and the cartridge should not make any clicking noises. After all these years, the original cartridges seem to be doing better than 3rd party ones.
Let’s start by opening the ribbon cartridge gently:
On the inside, you will see the big green main cogwheel that is turned by the printer. The ribbon is pulled through it and its smaller green counterpart. The ribbon is pulled across the green roll at the top right, which takes the ink from the sponge and rolls it onto the ribbon. Be very careful with the sponge, as it is very likely to disintegrate into smaller pieces due to its age! Don’t worry though if you end up breaking off small pieces, the cartridge should still work fine.
Note that there are four sponges stacked on top of each other for the four colors (black, magenta, cyan, yellow), or four black ones in a black-only cartridge. If you want to reach the other sponges, you have to be extremely careful. Don’t use tweezers, instead, get out the whole stack by turning the cartridge upside down, making sure the other components don’t fall out.
For refilling, you will need some stamp pad ink, like “Pelikan Stempelfarbe 84”. This 30 ml bottle can refill a cartridge dozens of times.
Cover the whole surface of the sponge evenly with ink. Wait for about a minute until the ink has been absorbed, and repeat a few times until it takes longer to absorb. Do not put any ink onto the ribbon: The ink is way too concentrated, and it will make the ribbon congeal so it can’t move any more!
When closing, make sure the roller at the top right it fitted correctly into the notch in the lid, which can be tricky.
The whole ribbon will have to be pulled across the sponge and the roller once or twice until you can see some effect. Use the following BASIC program to keep printing text in NLQ mode:
10 FOR I = 64 TO 95 : A$ = A$ + CHR$(I) : NEXT 20 OPEN 4,4 30 PRINT#4, CHR$(31); : REM NLQ MODE 40 PRINT#4, A$ 50 GOTO 40
After about a page of printing, the ribbon should be like new!