Table of Contents

[Making Cochineal Lake]

Name: Mellon Snyder

Date and Time: 

2021.06.01, 10:00 [am]

Location: Nuss Dorm, New York NY

Subject: Extracting Pigment from Cochineal

To begin, I’ll provide the recipes that we were provided in class:

RECIPE 1: “Standard”

Procedure:

• Grind cochineal in mortar and pestle
• Using a small utensil, add cochineal to the drawstring bag. Close the bag tightly
• Add potash and bag of cochineal to 300ml water in the 1000ml beaker
• Bring to a boil and boil for 15-20 min
• Using heat, dissolve 10g alum in 50 ml water in the 100ml beaker
• Warm the colored solution to about 50 ˚C and add alum solution very gradually, stirring. Do this slowly and incrementally, checking the pH of the solution after each addition until a pH of 6-7, there is no further effervescence, and precipitation of the lake pigment appears to be complete
• Allow the solution to settle for at least 15min (ideally overnight)
• Pour solution through filter in a funnel
• Once the liquid has drained through, wash the pigment: discard the filtrate and place funnel+filter over a clean container. Pour 100ml of clean water through the filter. Repeat until the filtrate is clear
• Allow the pigment to dry on the filter (at least overnight), then scrape off and use

RECIPE 2: “Standard - Reversed”

Procedure:

• Grind cochineal in mortar and pestle
• Using a small utensil, add cochineal to the drawstring bag. Close the bag tightly
• Add alum and bag of cochineal to 300ml water in the 1000ml beaker
• Bring to a boil and boil for 15-20 min
• Using heat, dissolve 10g potash in 50 ml water in the 100ml beaker
• Warm the colored solution to about 50 ˚C and add potash solution very gradually, stirring. Do this slowly and incrementally, checking the pH of the solution after each addition until a pH of 6-7, there is no further effervescence, and precipitation of the lake pigment appears to be complete
• Allow the solution to settle for at least 15min (ideally overnight)
• Pour solution through filter in a funnel
• Once the liquid has drained through, wash the pigment: discard the filtrate and place funnel+filter over a clean container. Pour 100ml of clean water through the filter. Repeat until the filtrate is clear
• Allow the pigment to dry on the filter (at least overnight), then scrape off and use

Of these two recipes, I decided to use Recipe 1: Standard.

To be honest, my decision to go with the standard recipe was guided mostly by the fact that “standard” sounder simpler, and because I was already intimidated by this process going in, I wanted to keep things as standard as possible!

You can see the two “beakers” (actually, shatter-proof mason jars) that I used here. Both are filled with appropriate volumes of water. The larger has the 300mL of water needed to extract pigment from cochineal, and the smaller has about 50 mL of water that I would dissolve my potash in.

Our cochineal came pre-ground for us, sealed in a fabric tea bag. So I was able to skip the listed step of grinding down the cochineal. I started out by placing the large jar of water in the pot, which had enough water itself to at least cover the level of water in the jar.

I’d like to note that before I heated the pot, the jar was already submerged. I think this is important to prevent any sudden temperature changes that might cause even shatter-proof jars to shatter. (I’m writing these notes after-the-fact, but my later experiment with extracting pigment from cherry juice showed me that these jars absolutely can shatter, and I’m glad I followed my instincts with this initial Cochineal learning experience. Not only are shattering jars dangerous, but they can cause you to waste precious materials).

I then added my alum to the jar of water and cochineal.

You can see that the pigment from the cochineal was already releasing quite well! There’s a pinky red-hue that looks quite promising.

Simultaneously, I was heating my smaller jar with 50 mL of water, which would be used to put potash into solution.

Look at that color! At this point, the cochineal soup has been cooking for about half an hour. The water is getting more and more pigmented, and here it’s nearly opaque.

At this point, I used chopsticks to lift the cochineal bag out of the water, and I gave the richly pigmented water a moment to cool. While it cooled (just down from the hot simmer it was at), I went ahead and dissolved my potash into solution in the smaller jar. When it’s in solution, the liquid should look totally clear and not cloudy. This is why we heated the smaller jar of water-- the heat helps to speed up the process of dissolving potash.

Here, now, I’m starting to pour the potash solution into my jar of pigment.

Here you can see a reaction beginning! I poured very very little of my potash solution into this jar, and it produced a good bit of foam regardless. I think it’s interesting that the foam is such a bright pink compared to the darker, richer pigment below. Is this the way that the foam refracts light, or does this foreshadow the color my pigment will turn in the end?

Once I had foam erupt, like in the previous image, I used the chopsticks to beat down the foam. When I had only stray bubbles remaining on the surface, like you see above, I added more of my potash solution.

More foam! Also, it’s interesting that the color of the bottom liquid is starting to change, too. It’s becoming a brighter pink that resembles the foam on top. Again, I beat down this mixture with chopsticks until the foam was at bay and barely visible.

For some reason, the last time I added potash solution (and just about the same amount of solution, I’ll note) the foam became much more aggressive. I’m curious what was happening here, chemically. Why didn’t addition of the (relatively) same amount of potash yield the same amount of bubbly reaction? In class, we talked about adding more potash solution until the reaction stopped occurring, but at this point I was entirely out of potash solution, so I had to stop where I was. I might have been able to produce more pigment if I had more.

Here you can see the pH earlier in the process (yellow, on top), versus later in the process (green, on the bottom). The first test was taken after some potash was already added, and I was wondering whether I should stop adding more. The second test was taken after I dedicated to continue adding potash, and I was curious where I was in terms of pH.

At this point, with my foam beat down and my potash all used up, there wasn’t much I could do but wait. I left my jar of pigment overnight to settle. You can see here the pigment has settled down on the bottom, and a layer of water has formed on top.

It’s useful to have a second mason jar of about the same size. You can see my setup here. I have the jar with my pigment, and beside it I have a clean jar set up with a funnel and coffee filter.

I then poured the mixture from the jar of cochineal pigment through the funnel, careful not to pour so much so fast that the filter ripped.

After about two hours, I had a nice goopy substance that would dry into a pigment collected in the filter. At this point, I wanted the goop to get more airflow and dry faster in time for tomorrow’s class. I carefully lifted out the filter, and placed it on top of some paper towels, by a window, to dry out.

By the next day, my pigment was dry! I put some on a table here, and you can see the more purplish hue it has adopted since drying. I’m curious whether this will paint out as being so purple, or return to its redder, pinker tones.