[bcsmg]

Hello there-
We're trying to figure out what kind of fluid would be used for the following: We're building a front door and it will have a glass circle at the top of the door.  We'd like to put in some kind of blue fluid to give off the illusion of water swishing as the door opens and closes.  He thought maybe it'd be a chemical of some sort--something that would LOOK like water, but something that wouldn't fog up the window, evaporate after time, mold, etc.  We know there are companies that probably use this in their products, but we really didn't know where to start... so here we are.  We did get SOME information from a chemistry teacher (her response is quoted below), but unfortunately, it's not enough of an answer.  Can anyone offer some advice on this?

Yes, I recall seeing a type of small device like (I think) you are describing; it was being sold in a science store or science fair, as I recall.  This device had a thin (1/8"?) layer of liquid sandwiched between two clear plastic or glass panes.  It was framed in wood, about 8" by 12".  When it was moved, the blue liquid inside rocked back and forth, giving the impression of ocean waves.  To a novice, the container appeared to be half-filled with a cobalt blue liquid.  However, it was actually filled with two immiscible liquids -- the bottom blue one and the top colorless one.  Sand, boats, clouds, etc were painted on the outside of the plastic.

I recall asking the person who made them if the bottom layer was water colored blue; he said no, but it was a polar compound with a salt added to make it blue.  I recall he said water wouldn't work because the boundary between the two liquids needed to be very crisp.  Also, water could eventually becomes cloudy with algae.  (Perhaps an alcohol could be used?)

Thanks for any help you can lend!

[jeffrey.struss]

I always used kerosense and blue colored water. It works quite well. Maybe a bit of ethanol/water mixture would work as well. I think a lot of salts are insoluble in ethanol.

Another option would be to use something like ethanol/isopropanol as the top clear layer and a lower layer using a heavier non-polar material dyed blue by a non-polar dye.

[Enthalpy]

I imagine silicone oil would be a candidate as one of the liquids. Durable, inert, very hydrophobic, wets glass. Dyes exist for silicone rubber.

Antifreeze (= ethylene glycol, currently being replaced by propylene glycol) is already blue. Too pale if thin?

If using water, additives may be desirable, like some antifreeze, and antibacterials and fungicides. Methylene blue? Copper (II) sulphate?