The Science Of Dying Easter Eggs

easter eggsI have kind of a weird obsession with eggs. Whether this derives from, or is the cause of, my love of birds is a literal “chicken and egg” question. Needless to say, Easter has always been my favorite holiday. Every year I hold an Easter egg decorating party at my house. I always try to find the Deluxe Paas kits that have at least nine colors because go big or go home. This year, I thought it would be interesting to learn something about how those dyes actually work.

When you buy the Paas kits, they come with small dye tablets and instructions to add one tablespoon of vinegar and a cup of water. So what is that all about?

The water seems obvious because you have to dissolve the dyes and provide enough volume to submerge your egg. It’s the vinegar that I find interesting. Vinegar is the household name for the molecule acetic acid. It’s a fairly mild acid in chemistry terms, which is why you can buy it at your local grocery store. For dying Easter eggs, that acidity is very important for two reasons.

First of all, egg shells are made of a compound called calcium carbonate, CaCO3, which dissolves in acid. When you let the eggs submerge in the diluted acid mixture, it causes the surface to dissolve. That both creates more surface area for the dye to stick to and exposes part of the underlying cuticle of the egg. The cuticle is made up of a lot of different proteins that gain a positive charge from the acid.

Which gets us to the second part—most pigments used to dye eggs are negatively charged. Just like the North end of a magnet will attract the South end of another, the negatively charged dye becomes attracted to the positively charged proteins on the eggs. That allows the dyes to stick to the shells, giving Easter eggs their vibrant colors.

So why not just make the dye mixture in pure vinegar? As a writer from Wired Magazine found, the Paas company did it’s research to assure the best egg dying results. If you don’t add any vinegar at all, the eggs get a pastel, washed out color. But if you add too much vinegar, the CaCO3 begins dissolving too quickly. That makes a lot of bubbles that cause the dye to streak or not stick at all. So to achieve the even, vibrant color I like for my eggs, the Paas instructions are exactly right.

One complaint I’ve heard from my friends is that they hate the smell of vinegar, which begs the question—are there other household acids that would work just as well? Science Friday, one of my favorite podcasts, actually did a series of experiments with other household acids. They found that you can just as easily replace the vinegar with orange juice (citric acid), aspirin (salicylic acid), and vitamin C (ascorbic acid). So if you don’t like the smell of vinegar, there are other options out there for you.

As for me, I am just glad to know that I have the optimal egg dying conditions for me to decorate what will eventually become entirely too many trays of multicolored deviled eggs.

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