-1
$\begingroup$

I am looking for pigments that at first are not showing their colour (and appear colourless), but after adding water or another 'component' like oil/alcohol etc. will show their colour.

My excuses for not knowing the right terminology and terms. I have little experience with Chemistry

$\endgroup$
1
  • 1
    $\begingroup$ All kinds of "magic inks" have that property (typically, you add something other than water, like acid, base, or heat). $\endgroup$
    – Karsten
    Jan 8 at 22:20

1 Answer 1

8
$\begingroup$

First, do you definitely mean "pigment", rather than "stain" or "dye"?

Second, there are many dyes, stains and pigments that change color when dampened. The do so in a number of ways.

  • Finely-ground transparent substances, such as powdered colored glass, often look white or just a pale version of the bulk color because of internal reflection and refraction of light. Dampen them, and the water lowers the change in refractive difference between the substance and air. As soon as water evaporates, the powder pales.
  • Chemicals may change color when water of hydration is added. Anhydrous copper sulfate, $\ce{CuSO4}$, is white. As it's commonly sold, the copper sulfate pentahydrate, $\ce{CuSO4.5H2O}$, is blue. Heat it to dry it, and it reverts to white.
  • Chemicals may combine irreversibly, changing color when wet, and staying that color even when dried. For example, ferric ammonium sulfate, $\ce{NH4Fe(SO4)2.12H2O}$ is grayish-white, and potassium thiocyanate, and potassium thiocyanate, $\ce{KSCN}$ is colorless. If the two are kept dry, the mixed powders are white, but a drop of water turn them red, permanently.
$\endgroup$
2
  • 3
    $\begingroup$ Glazes for pottery are powered glass. It is difficult to anticipate the vibrant colors achieved after firing from the mute colors when applying the glaze. $\endgroup$
    – Karsten
    Jan 8 at 22:18
  • 1
    $\begingroup$ @Karsten, exactly! The powdered frit merges into one surface. $\endgroup$ Jan 8 at 22:26

Not the answer you're looking for? Browse other questions tagged or ask your own question.