A chemistry professor at Catholic University, Bunce likes to bring science to life for her students through holiday-themed demonstrations. On April 19, she’ll explain the chemistry behind Easter egg dyeing at Mount de Sales Academy in Catonsville, Md., as part of the USA Science & Engineering Festival’s “Nifty Fifty (times two)” program. So what is the chemistry behind egg dyeing?
There’s a protein coating on the egg shell, and we have to get the negative molecule in the dye to attract to that protein, so we put a positive charge on it — that’s where the vinegar comes in. Vinegar is a very mild acid that releases positively charged hydrogen ions. You could dye eggs with hydrochloric acid instead, but that wouldn’t make them very edible.
What kind of vinegar makes the brightest eggs?
It doesn’t matter, actually. And if you run out of vinegar for your egg bath, substitute lemon juice, because it’s citric acid. In most cases, water out of the tap is slightly acidic, too.
Clever! How can we harness the power of science to dye the most enviable eggs on the blocks?
Put a design on the egg with a crayon first. Crayon is mostly wax, which doesn’t dissolve in water — scientifically speaking, it’s nonpolar. The dye won’t adhere to the egg where the crayon is, so the pattern will remain after you dye the egg. There’s another trick we do, when you can’t tell if the egg in the fridge is hard-boiled or raw. It’s called the “spin test.” When you spin a cooked egg, everything is solid and moves in the same direction as the egg shell. But a raw egg won’t spin as well, because the contents are liquid and resist the direction of the egg shell’s movement. Just another quick trick brought you by the letter “S” for science!
