Q&A for How to Make Invisible Ink with Baking Soda

The beetroot acts as a pH indicator. A pigment in the beetroot called betanin reacts with alkaline/basic sodium bicarbonate, resulting in a deep purple color.

If you use blue filters, yes, as the purpose is to use blue light (higher frequency light waves). This can sometimes be achieved with sufficient thin blue surfaces layered over the light. Using a flashlight would be easiest -- superimpose translucent purple and blue sweet wrappers.

Nope. UV lights are usually what has to be used; while a UV light may be purplish, it's a very different kind of light from a flashlight with a purple tint.

If a baking soda solution will work, a table salt solution will work, too.

No, it would cause a stain and would not be invisible.

No. This method works because of an acid-based chemical reaction that food coloring wouldn't cause.

It does not have to be fire, it just has to be hot enough to heat the ink. Try using a hair dryer or a iron.

No it won’t make it much easier to read. Lemon juice is what you write with, and the grape juice reveals the baking soda solution, so it won’t work.

Possibly around 10 minutes. Don’t worry, it will dry quite fast. You shouldn’t dry it with an iron as it will make the letters appear.