Watermarks

Just another simple question: When I was collecting in the 1950's, I had an actual black glass watermark tray, and, under the tutiledge of my uncle, actually used H2O in the tray to find the watermarks. I never heard of, during that time, such a thing as "watermark fluid". Did it exist back then, or was it common practice to use water in the mid-50's?

Also...for MOG stamps, will the currently available watermark fluid preserve the OG? I'd also ask for comments on using actual water vs. watermark fluid on used stamps, assuming one has a decent "drying" book.

Larry