[Not a Kemist]

I'm here to find out if this is even possible.
I've searched the web, YouTube, etc many times for this. Generally I just find the iodine clock reaction.

I want to have an opaque liquid that with the addition of another liquid or powder will turn it clear enough to see something behind the container.
Something safe and something that will require minimal or no stirring or shaking... since the container will be stationary.

I've turned Coca Cola somewhat clear with bleach and this would work but something without the overpowering smell of Clorox would be preferred.

Is this even possible or am I wasting my time in this search?
Thank you.

[wildfyr]

There are dyes that would be very colored at one pH and clear at another.

Crystal violet lactone comes to mind. It will appear dark purple in the presence of acid, but with addition of a mild base like bicarbonate will go clear.

[Not a Kemist]

There are dyes that would be very colored at one pH and clear at another.

Crystal violet lactone comes to mind. It will appear dark purple in the presence of acid, but with addition of a mild base like bicarbonate will go clear.

Could you give me a few more details on the preparation of this? What exactly do you mean in the presence of acid? What would I be mixing the lactone with?
As for the bicarbonate... sodium... potassium?

Would this be usable for the crystal violet lactone?
https://www.amazon.com/Innovating-Science-Bacteria-Stain-Chemicals/dp/B01K5S6DNO/ref=sr_1_fkmr2_2?keywords=Crystal+violet+lactone&qid=1564527799&s=gateway&sr=8-2-fkmr2

[wildfyr]

If you take the specific molecule crystal violet lactone and put it in a weakly acidic solution (a bit of HCl in acetone would do) then it will be very dark purple. If you add some sodium or potassium bicarbonate, or just some NaOH to prevent fizzint, it will go clear.

No, that is plain crystal violet, you need crystal violet lactone.

There are other dyes that may work, look up halochromic dyes.

[Enthalpy]

[...] with bleach and this would work but something without the overpowering smell of Clorox would be preferred [...]

One smell-free oxidizer is called sodium "percarbonate", a co-crystal of carbonate and hydrogen peroxide. Available in shops under varied names.
https://en.wikipedia.org/wiki/Sodium_percarbonate
https://en.wikipedia.org/wiki/OxiClean

[Enthalpy]

Does the application need a liquid?

Making a surface black or transparent can be faster, reversible, more opaque. LCD displays do it routinely, big surfaces exist.

[Enthalpy]

Or could something let a dispersion settle, or a colloid coagulate? Some small additions let sauces separate. Little lemon juice lets fats separate from water in milk. Indian ink for instance is opaque already in small concentration.

[Not a Kemist]

If you take the specific molecule crystal violet lactone and put it in a weakly acidic solution (a bit of HCl in acetone would do) then it will be very dark purple. If you add some sodium or potassium bicarbonate, or just some NaOH to prevent fizzint, it will go clear.

No, that is plain crystal violet, you need crystal violet lactone.

There are other dyes that may work, look up halochromic dyes.

Ok, thanks. I'll have to try to find a place that sells these things so I can give it a try.

[Not a Kemist]

[...] with bleach and this would work but something without the overpowering smell of Clorox would be preferred [...]

One smell-free oxidizer is called sodium "percarbonate", a co-crystal of carbonate and hydrogen peroxide. Available in shops under varied names.
https://en.wikipedia.org/wiki/Sodium_percarbonate
https://en.wikipedia.org/wiki/OxiClean

Thank you. I'll give that a shot... also, yes for what I'm doing I'd prefer to have a liquid doing the color change.

[Enthalpy]

Permanganate solutions are violet, darker as the concentration increases. Hydrogen peroxide, including at pharmaceutical 3% concentration, together with reasonable acids, discolour them.
https://www.youtube.com/watch?v=Kln0v_L5ExE
https://www.youtube.com/watch?v=8MRpdwH0ArA

[wildfyr]

Permanganate solutions should be handled with considerable care.

However, this is a pretty darn good idea, very easy to access the materials.