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Note: if Inky Recipes is a more appropriate forum, perhaps a moderator could move this post? I'm experimenting with ink flow improvement, as my BSB is very hard starting, and dries nearly solid in the feeds/nibs of my pens. I gather the first thing to do is add a preservative, because whatever else I add to the ink may increase its susceptibility to contamination. I thought phenol, quaternion-15, or phenoxyethanol would be a good choice. Phenoxyethanol, though relatively untested, was the only preservative I could buy locally (after ruling out the common food preservatives, which are no good in alkaline liquids). (Chloroxylenol is very easy to get, and I wonder whether it would work.) The phenoxyethanol I bought was combined with ethylhexylglycerin, which is a surfactant. I need to increase the ink flow, but not by adding a huge amount of surfactant! (I'll be adding 0.5% preservative, but I'll start with only 0.0001% nonionic surfactant. Obviously I don't want to add too much!) I couldn't find any online references to ethylhexylglycerin in ink, so I set out to find out whether it significantly changes surface tension. I measured about a drop of preservative as 15 mg, then diluted it with water to around 3.2 g total, to get 0.5% preservative. I mixed and used a pipette to drop six drops of water, then six drops of mixture onto a clean plastic surface. I examined the contact angle with a magnifying glass, and could not tell the difference between the two groups. As an additional control, I mixed half a percent of dish soap into water and examined six drops. They spread, and looked nothing like the other two groups. (In this photo, the soap is nearest the camera. The batch with the disinfectant is in the middle.) My conclusion: despite being a surfactant, a modest amount of ethylhexylglycerin does not noticeably change the surface tension of water when used at normal rates as a preservative. It is thus not likely to have a large effect on ink flow. (Flow is not directly caused by surface tension, but there is some relationship. To see the difference, read about how "super spreaders" do not have the lowest surface tension.)