A color changing strip mounted on the exterior of your Invisible Ink well, that indicates the level of invisible ink in the well. There are pigments that are sensitive to temperature differences. An adhesive strip impregnated with this type of pigment is attached to the exterior of the bottle or pen and shows a color change at the level of the ink.
Or you could just float something on the surface of the ink. (thank you [sufc])-- ato_de, Jul 03 2003 Disappearing Ink Pen: http://www.pimall.com/nais/dispen.htmlFabric marker pens for sewing are less expensive than this one. [Amos Kito, Oct 04 2004, last modified Oct 05 2004] How does it work?-- angel, Jul 03 2003 Something that floats on the surface of the ink.-- sufc, Jul 03 2003 a little rubber duck would be cute-- po, Jul 03 2003 Pass quickly back and forth over open flame, shall disappear again when cooled-- ty6, Jul 03 2003 [ty6], in this idea, you'd know before writing whether or not you have invisible ink... or other transparent fluid.Can't you tell while writing, by a slight sheen -- like writing with water? Disappearing ink pens [link] also leave a reappearing residue. Write normally with this ink, even, I'd suppose, if it's in an inkwell. But it may not disappear fast enough for your purposes.-- Amos Kito, Jul 03 2003 So...
I'm writing a missive to my Lackies,in invisible ink, and I start wondering: Why do I keep using the same stupid lackies? The last time I tried to take over the world, half of my followers were not in position, and the other half were missing some of their equipment. You just can't find good help these days, and it is sooooooo embarassing to send out an ultimatum to all of the world leaders, only to discover that you don't have a guidence system for your ultimate weapon.
Turns out I was out of ink, one more plan shot to hell, back to the old drawing board, with a full ink-well.-- ato_de, Jul 03 2003 Why not just write your missive on a computer, then print it on a laser printer loaded with invisible toner? Or you could email it in an invisible font.-- AO, Jul 03 2003 what about just having a blue ink that turns invisible when it dries.-- neilp, Jul 05 2003 Now if I could just find where I put the jar...-- RayfordSteele, Jul 05 2003 random, halfbakery