Ah, springtime and the beautiful colors that return to our temporarily anemic post-winter world. Whether it’s in the tulips, daffodils and crocus or the delightful blue robin eggs, springtime represents color. In fact, for those who celebrate Easter, we can take the idea of “color” to great extremes as we find ways to turn modest chicken eggs into incredible creations. Some of the most ornate Easter egg designs, known as pysanka, actually come from Ukraine, where various layers of dye are applied using intricate patterns of wax-resist.
As we continue celebrating the International Year of Crystallography, it seemed only natural to think about tint as we chose our Crystal of the Week. That’s how we arrived at an ancient dye, Tyrian purple, which has been used to color garments, beads and many other textiles since the time of the Phoenicians. This shade of purple is also known as “royal purple” because at one point the dye was so expensive to produce that only royals could afford it. Just a few grams of powdered Tyrian purple requires tens of thousands of snails (yes, snails!), which explains why the dye was so expensive in antiquity, at one point costing its own weight in silver!
Beautiful as it may be, the most interesting aspect of Tyrian purple is its preparation. Like all mollusks, predatory sea snails secrete mucus aka “snail slime” to protect their tissues. Unlike other mollusks, the mucus of predatory sea snails (family name: Muricidae) can be distilled to a vivid purple dye. Although Tyrian purple preparations initially yield a liquid product, the water content can be evaporated to produce a purple powder, like that shown in the image. Of course, the granules in the powder are tiny crystals of the molecule that gives snail slime its purple hue. Many other common dyes are prepared similarly, where the crystalline powder is easily solubilized in water to dye clothing or other textiles or mixed directly into paints and plastics.
Unlike many dyes, which fade in sunlight, Tyrian purple actually becomes brighter and more vivid. In the early 1900s, the dye molecule was shown to be a type of organobromine compound. Other common organobromine compounds include some fire retardants, biocides and pharmaceuticals. And if you’ve ever taken analytical chemistry, you’re probably familiar with bromothymol blue, a common pH indicator.
But all of this talk of dyes and dye preparation actually brings us back to Easter eggs! Did you know that a variety of common kitchen items can be used to prepare different dyes in beautiful hues? Diluted grape juice delivers lavender, while red wine and the blossoms of violets yield a purple-blue. Boiled red cabbage, canned blueberries, or concentrated purple grape juice all create shades of blue. Boiled spinach can be used for green, while many spices (e.g., celery seed, ground cumin, ground turmeric) produce yellow when boiled. Coffee and tea can deliver brown hues. Orange can be obtained from paprika or cooked carrot. Beets and raspberries yield beautiful shades of pink. Otherwise, using more concentrated raspberry juice or pomegranate juice gives red.
Okay, so perhaps our obsession with dyes this week goes beyond crystallography, but the extended winter finds us craving color a bit more than usual this spring. Whether your favorite hues come from crystals, spices, vegetables or snails, may they brighten your springtime days.