Natural Dyes and Pigments

Hope Leeson recently joined the Nature Lab as the Botanist-in-Residence, where she supports the botany and the biomaterials work at the Lab. For the next couple of months, we will share narratives from Hope that detail her exploration of natural dyes and pigments.

Playing with pH; Making Ink from Blood Orange Peels

"Continuing the theme of pigment from compostable food scraps, I experimented with the peels of blood orange, with the goal of making an ink. Blood oranges (Citrus x. sinensis) originated in Spain, as a natural cross between the grapefruit (which is also a hybrid: Citrus x. paradisi), and the tangerine (Citrus tangerina). They have such a deep red color in the skin that I was curious what color they would give as an ink.

I started with 1 cup of chopped orange peels and 2 cups of water. The color in the dye pot was a beautiful orange, as you might expect, but then I began to play by taking a small amount out of the dye pot and adding ingredients to see how changing the pH might change the color. I liked the color shifts, and luckily, I had been drying and saving blood orange peels for a few weeks, so I had enough for three small batches of dye. To each, I added a small amount of different ingredients to shift the color of the bath.

To see the color and intensity of the dye as an ink, I painted each dye onto Strathmore watercolor paper, in four layers. Strathmore says the paper is ‘acid free’, but does not claim to be pH neutral. The colors were so varied and reacted with the paper in ways that I didn’t expect, that I also decided to dye various fabric swatches to see how they took on the color. To each dye pot, I added small swatches of wool, silk, linen, cotton, and canvas.

Here are the ingredients for each of the dye baths:

—1 cup blood orange peel, 2 cups water + 1 teaspoon washing soda pH 9; dye color dark green
—1 cup blood orange peel, 2 cups water + 1 teaspoon aluminum sulfate (alum) pH 4; dye color dark pink
—1 cup blood orange peel, 2 cups water + 1 teaspoon white vinegar + 1 teaspoon salt pH 5; dye color orangey-pink

The dye bath with washing soda, was a dark green color in the dye pot, and gave a richly pigmented color as an ink. The alkalinity in the soda really broke down the peels which allowed the most pigment to become soluble in water, of the three baths. To my surprise, the dye painted onto the watercolor paper as a deep yellow, which built up to a golden-orange with increased layers. As with the paper, the fabric swatches each took on variations of soft yellow.

The alum dye bath which was dark pink in color, held little pigment in the water, and painted on as a thin pink, which then seemed to react with the pH of the paper, turning green as it dried. As I painted successive layers, the pink color was able to stay a while, and created a green with pink on top, adding to the depth of the pigment. The fabric swatches, all came out with beautiful shades of pale pink.

The dye bath with vinegar and salt, was an orangey-pink color that reminded me of the color of the juice I squeeze out of pink grapefruits. The ink pigment was more saturated than that of the alum ink, and painted onto the watercolor paper as a decidedly intense minty green, with each layer darkening as the pigment built up. The fabrics all took on the same soft green colors.

All of these swatches (water color paper and fabric), and many more, are stored in the Natural Dye Library at the Nature Lab." — Hope Leeson

Making Avocado Pink; Ink from Avocado (Persea americana) Pits

"Inks have traditionally been made from just about any substance on the land that had a pigment to give: shellfish, insects, insect galls, plant seeds, leaves, and roots, charred bone, iron, and soils have all been used by humans around the world to extract lasting color. Historically ink was a concentrated pigment from a dye that was thickened and preserved.

Both the skin and the seed (pit) of the avocado fruit are rich in tannins, and have been used for thousands of years as fabric dye and ink. The tall tree, known scientifically as Persea americana, has origins in central Mexico, and has been cultivated for its’ fruit since 5,000 BC (Galindo-Tovar et al., 2007). Oral histories of the Kuna people in northeastern Panama, tell of avocado being used to dye the fabrics in their creation story, and wool fragments dyed with avocado pit have been found in Andean caves, where the Quechua and Aymara people lived (Verde, 2019). Thanks to a long history of cultivation and importance to the people of South and Central America, and the West Indies, there are three recognized landraces of the avocado, and numerous varieties developed by horticulturalists from these; all with apparently slightly different dye properties (Verde, 2019).

The Hass avocado is the most commonly available variety here in Rhode Island, and since late winter is the season for avocado ripening, they have been plentiful in the markets. I wanted to experiment with their dye and chose to start with the pits.

To make the dye I chopped fresh seeds into half-inch chunks (caution – if you postpone chopping the seeds into small pieces, they will dry out and become rock hard, so chop them up and store them dry while you build up your supply!) and then ground them in a food processor. For storage, I heated the ground seed on a cookie sheet in the oven for half an hour at 170 degrees. For a 4-ounce batch of ink you will need about ½ cup of ground avocado pits (3-4 seeds).

Avocado color is pH sensitive, so you can create a range of colors from a pale orange to a deep blood-red color. Water can play a big part in the varying pigment colors, depending on the pH and also what other minerals are present (Verde, 2019).

I tried three pH variations to see what colors I could achieve. The first was simply avocado seed in my well water (solution pH 6). The second was avocado pit with aluminum sulfate (alum), which had a pH of 2. The third combined soda ash (washing soda) with the avocado (pH 12). The most intensely deep red color came from the soda ash solution, while the more acidic solutions were more pale and orange. Avocado alone with water gave a beautiful pale orange-pink color.

After simmering the mixtures for 20 minutes, I let them cool overnight and then filtered the sediment out of the liquid, and added a few drops of clove oil to each as a preservative. I then mixed up a solution of gum arabic and added 50% by weight to a sample of the dye. I think 25% is probably sufficient, but with a greater percentage of gum arabic you can achieve a lacquer-like texture on paper, with a really luminous color. You can also use egg tempera as a binder. The purpose of the binder is to hold the pigment in suspension and to create a more viscous liquid. Vinegar and alcohol are also used as preservative." — Hope Leeson

Here is the recipe Hope used:

For the ink base:

—½ cup ground avocado pits
—1-cup water
—Simmer for 20 minutes, then cool overnight.
—Strain the liquid and then filter through a coffee filter to remove fine sediment.
—Add 3 drops clove oil

For gum arabic solution:

—22 grams ground gum arabic
—44 milliliters freshly boiled distilled water (pH neutral)
—Stir in freshly boiled water to dissolve gum arabic powder. This can take a long time to fully dissolve.
—After about 24 hours the solution will be clear (no longer cloudy) and is ready to use.

For the ink solution:

To 100% of pigment (whatever amount you measure out)

Add 25% gum arabic binder.

Example: 10 grams of ink

2.5 grams (about ¼ tsp.) gum

References:

Galindo-Tovar, María Elena; Arzate-Fernández, Amaury M.; Ogata-Aguilar, Nisao & Landero-Torres, Ivonne (2007). Harvard Papers in Botany. 12 (2): 325–334, page 325

Verde, Isvett, July 15, 2019. New York Times, Avocado Dye is, Naturally Millennial Pink.

Making a Lake Pigment from Pomegranate (Punica granatum) Skin

"A 'lake' pigment is a dye that is mordanted onto a mineral salt, making it insoluble in water. The word “lake” in this case, is derived from the name of a group of scale insects, called “lac scales”, which have historically been used to make pigments as well as shellac and varnishes.

The pink skin of pomegranates can be used to make a yellow or yellow-green dye, as well as being used as a mordent because of the tannic acid held in the skin. From a botanical aspect, I find it interesting that pomegranates are in the same family (Lythraceae) as the tree known as Henna (Lawsonia inermis), which has leaves that make a range of reddish-brown hues.

To make the lake pigment, I first simmered 25.0 grams of dried pomegranate skin in 500 milliliters of water for 20 minutes. I then dissolved into the hot water bath, 25.0 grams of aluminum sulfate (alum), and continued simmering the bath for another 40 minutes. The liquid was clear and a very deep red color. Alum made the solution very acidic. Pomegranate skins + water had a pH of 7.0. With the addition of alum, the pH shifted to 1.0. After 40 minutes of simmering, I strained the dye bath through a fine cloth to remove any particles of the pomegranate skin. The Pomegranate-alum dye gave a greenish yellow color to watercolor paper.

I then mixed 20.0 g of soda ash (washing soda/sodium carbonate) into 250 ml of hot (just boiled) water. I poured the dye bath into a tall glass jar and added a small amount of the soda ash solution. The basic pH (11.0) of the soda ash reacted with the acidity of the pomegranate solution and immediately started fizzing as the carbonic acid was released from the solution as a gas. I continued stirring down the bubbles and adding more soda ash solution until all 250 ml had been added to the dye. The dye was now a cloudy yellow-green color, and had a pH of 10.0. Pigment was beginning to precipitate out of solution, and I left the jar sitting overnight to complete the process. In the morning I poured the pigment and water through a coffee filter. It took all day to filter through. Over the course of three days, the pigment gradually dried, and became black in color and very hard and brittle. When it was completely dry, I scraped the lake pigment off of the filter and ground it into a fine powder with a mortar and pestle. The powder is now a yellow ochre color. Since the pigment is no longer soluble in water, I’ll need to combine it with a binder. In this process, the pigment will be ground even more finely to make the paint. Binders like gum arabic or egg tempera are typically used, and the paint should give a warm yellow color."