recently, I have been doing some small experiments on "invisible words" to share some personal feelings.

"invisible text" refers to the phenomenon that the handwriting on the paper is colorless at first (or the color is indistinguishable from the background), and then the handwriting is clearly displayed in some way. The way to show color can be to add another solution, or it can be heated or illuminated with ultraviolet light to show fluorescence, and so on. In such small experiments, it is most common to write with one solution and then add another solution to develop the color. For example, an acid /base solution can be used with an acid-base indicator, or two substances can be combined to form a dark complex.

the following are some of the schemes I have tried:

Ferrous sulfate solution to write, color with tea containing tannins (see: dynamic picture appreciation: three kinds of "invisible text" most suitable for playing handsome)

phenolphthalein (ethanol solution, insoluble in water)

is not complicated, and pure discoloration can be easily realized in solution. the main factors that affect the effect of "invisible text" are the paper used and the way of applying "coloring solution".

first of all, the effect of paper with better water absorption will be better. Ordinary printing paper feels the worst, because it absorbs water slowly, and the applied "chromogenic solution" is easy to stay on the surface of the paper, making the handwriting and patterns unrecognizable. Relatively speaking, painting paper is better. Filter paper is the best in terms of water absorption, but also because of its excellent water absorption, words must be written with a very fine brush, and the handwriting is easy to faint. In addition, such as ferrous sulfate, lemon juice written on the paper will have a slight yellowing traces, so with not so white paper will be better.

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the next important thing is the way in which the chromogenic solution is applied. In the actual attempt, it is found that the handwriting is easy to blur under the scouring of the chromogenic solution, and one of the safest ways is to spray the solution carefully with a spray can. Do not spray directly at the paper you want to color, draw a little distance and let the water mist fall gently on the paper, so that it is easiest to keep the color of the handwriting in place. The handwriting effect shown in this way is as follows:

I have also tried to smear the solution with a cotton swab. Generally speaking, this also requires the water absorption of the paper, and the effect of filter paper is better. The paper with poor water absorption is still worried that the solution will float on the surface, and the written handwriting will be daubed back and forth.

also found a surprisingly good way to develop color: soak the paper written in phenolphthalein directly in sodium hydroxide solution:

of course it will burn off for a long time, but the handwriting is really very clear in a short time. However, this can not be taken out of the solution for observation, and the handwriting will be completely pasted in the process. Other experiences: ① ferrous sulfate solution is easy to oxidize and can be used with it. After writing, it can be dried quickly with a hair dryer. The color of ferrous iron will be more yellow when it is turned into trivalent iron, which is too obvious on paper. ② butterfly bean flower water must be very strong, the solution looks as blue as ink to show enough obvious color on the paper.

generally speaking, I think the general solution for this kind of experiment is to write with a solution on a drawing paper with good water absorption, and then spray the chromogenic solution gently with a spray can after drying. Of course, if you just heat or color in the way of ultraviolet light, then there will be no such problems. If there are any new ways to play, you are welcome to share ~