On Mon, 27 Jan 2020 09:04:11 -0500, J-J wrote:

However, just for testing, I cannot seem to find a low cost slow drying
ink. There is "barograph ink", but it is quite expensive for a tiny
amount. I know there must be alternative slow drying inks out there
with different names at less cost that might be suitable. Any
suggestions would be welcome here.

I used a barograph when I was at school 60 years ago. The ink was
water based and fed to a metal stylus through a flexible plastic tube.
The tube occasionally got blocked. I just blew down the tube to clear
it out. It made a blob on the chart. The ink didn't dry. It just
soaked into the paper.

Steve

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