When mixed with pure ethanol, the sandarac ink has a slightly yellow color depending on the mix ratio, but over the last few months, the ink inside the printer turned green, which shouldn't be happening.

Since yellow mixed with blue gives us a green color, I suspect that the blue color from the housing of the ink tank got dissolved by the ethanol and mixed with the ink. This already happened before when I used blue colored PU tubes for testing out the falling ball viscosimeter. After a while the transparent ink turned blue from the color of the tubes.

Since the green color is an unwanted ink contamination, I started cleaning the system by flushing out the green ink.

Here you can see the green ink compared to highly concentrated sandarac ink.

To prevent discoloration in the future, I got a new tank made out of white Polypropylene.

Unfortunately, the new one is no longer transparent. To still see the fluid level of the tank, I added a fluid level indicator to the side of it (just a 4mm PE tube).

When I disassembled the old tank, I found fittings with a suspicious blue color on top of the PTFE tape close to the tank.

After I connected the new tank I flushed the system with pure ethanol and loaded it with fresh ink.

After loading the new ink I let it sit inside the machine for a week of vacation.

When I came back, I saw that a certain part of the tubes had turned green again.

The chances that the blue color from the anodized aluminum had also turned the ink green were lower than that of the tank housing, but to eliminate all risk, I ordered new fittings to replace the blue anodized parts.

When I disassembled the fittings, I saw that there was also a lot of blue residue inside them. Since the ink is not corrosive I could rule out that it was a sign of brass corrosion. Instead, I think it could either be color from the anodized fittings or just a buildup of the blue pigments from the tank housing that got stuck on the fitting walls.

When the new fittings arrived I once again cleaned the printer and loaded new ink into it.

I mixed 500ml of new sandarac ink and loaded half of it into the printer.

But when I came back to the machine a day later, the same tube turned green once again.

I'm currently suspecting that there is still some residue on the walls of some fittings, which turns the ink green, and that after more flushing, it will disappear at some point, since there are no more colored parts in the system.