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Archive for May, 2014

Paintings made with homemade pigments for my Intersession Science and Art class

Paintings made with homemade pigments for my Intersession Science and Art class

As a follow up to our lab for making iron-gall ink, I wanted to find recipes online for turning a standard high school chemical inventory into paint pigments for watercolors, pastels, or oil paints. I found some websites that use natural ingredients such as berry juice or even walnut shells, but not much on how traditional paint colors were made or how to make them today so they are colorfast and lightfast.

Lemon yellow pigment made from a double replacement reaction of barium nitrate and potassium chromate.

Lemon yellow pigment made from a double replacement reaction of barium nitrate and potassium chromate.

To make an ideal pigment, it must have several properties. It must be suspendable in some sort of medium, such as water or linseed oil. This means it forms fairly large particles that are opaque to light yet small enough to not settle out of solution immediately. Once on paper or canvas they should resist re-dissolving (waterproof) in the case of watercolors but be re-workable in oil paints. Pigments must stay the same color under a wide range of circumstances, including minor changes in pH or humidity or under exposure to light.

The Villa of Mysteries in Pompeii. The red background color is vermilion, or mercury sulfide made from cinnabar. According to Pliny the Elder, the painters made a nice side profit by frequently washing their brushes and taking home the wash water.

The Villa of Mysteries in Pompeii. The red background color is vermilion, or mercury sulfide made from cinnabar. According to Pliny the Elder, the painters made a nice side profit by frequently washing their brushes and taking home the wash water.

Many paint pigments were originally made from colorful rocks or minerals, such as lapis lazuli, aquamarine, charcoal, orpiment, or cinnabar. Some of these minerals, such as cinnabar (mercury (II) sulfide) are toxic. Most of the red pigments tend to be this way, or else aren’t a very bright shade of red. Yes, iron oxide (rust) makes a reddish brown and madder root makes a dull burgundy, but only cinnabar (also known as vermilion or Chinese red, which is a bright orange red) or lead oxides (known as minium) could produce a good red until the Spanish Conquest of the Americas.

Chinese red lacquerware box colored with Chinese red, or cinnabar.

Chinese red lacquerware box colored with Chinese red, or cinnabar.

When Cortez conquered Mexico, he found an abundance of cloth dyed a bright red color and on investigation found that the dye was produced from a ground up insect called cochineal. It produced a range of bright reds from magenta through red-orange, depending on how it was treated. He brought samples of the cloth and the bug (along with samples of chocolate, but that’s another story) back to Spain with him. The insect grows on a particular species of prickly pear cactus in Central and South America, and the Spanish eventually found it could grow and prosper in some parts of southern Spain and on the Canary Islands. The dye it produces is called carmine. It is the red of a cardinal’s robes and the red of the British Redcoats. It is still used today, including in various types of red or pink-dyed foods, including strawberry milkshakes. In the food industry, it is known as Red Dye # 4.

Cochineal insects living on large cacti. The female insects are sessile, attaching themselves permanently to the cactus and extruding a waxy coating to prevent dehydration. The carminic acid helps to ward off predators.

Cochineal insects living on large cacti. The female insects are sessile, attaching themselves permanently to the cactus and extruding a waxy coating to prevent dehydration. The carminic acid helps to ward off predators.

The types of reds used for painting now are cadmium red (which is rather expensive to make) and alizarin crimson, a synthetic pigment made from coal tar derivatives. You can also get a pink color by using a hydrated form of cobalt chloride as a pigment, but it turns bright blue as it dries out.

Grinding dried cochineal insects to make carmine pigment. This dye is also used in foods. Yes, you are eating bug juice.

Grinding dried cochineal insects to make carmine pigment. This dye is also used in foods. Yes, you are eating bug juice.

After searching all this out, I finally came across a website that provided information on the history and production of various pigments. It is called Pigments Through the Ages and has a URL of: http://www.webexhibits.org/pigments/. It shows all the various colors made, gives the history and traditional methods for producing them, as well as modern equivalents. I determined to try these out in my chemistry and Intersession classes. We did some experimentation and here are the recipes we developed:

Pigment recipes

Once we got a viable pigment, we added a few drops of gum Arabic as a binder and to thicken the pigment. Then we tried it out by sketching and painting illustrations. My chemistry class had to paint something related to the history of chemistry or their own chemistry presentation topic.

Chemistry student Evan makes synthetic yellow ochre pigment.

Chemistry student Evan makes synthetic yellow ochre pigment.

Please feel free to experiment, adapt, and test these formulas. From our experiments we had some interesting results. The Cobalt blue recipe was a light purple/pink in solution (the hydrated cobalt chlorides) but dried a bright cyan blue color. This happened every time we made it in class, yet one student who wanted to test these pigments as a science fair project made her own cobalt blue which turned out staying a medium blue as the recipe said it should. I’m not sure what she did differently. When we made the cobalt purple, the student wanted to thicken the resulting solution by boiling off some of the water. This produced a bright pink pigment that was colorfast and was very useful combined with lemon yellow to make a flesh tone.

Making cobalt blue pigment.

Making cobalt blue pigment.

The lemon yellow and Prussian blue formulas are infallible. The yellow ochre recipe was interesting. It starts with the same cobalt chloride as two other pigments, but uses glacial acetic acid to convert it to yellow. It works to make a powder and then hydrate it once the process is done, producing a pigment that is a dull yellowish gray dry but makes an intense slightly grayish yellow when dissolved in water. The carbon black (India black) was easily made from finely ground charcoal, although I would use a charcoal without self-lighting fluid. It makes an oil slick on the pigment. You could probably use soot even more advantageously as it is already finely divided. Just build a small campfire and put a piece of metal over the flames to collect soot, then scrape it off for a pigment.

Making pigments in the lab at Walden School

Making pigments in the lab at Walden School

The colors we had trouble with were browns and reds. I have not tried making a pigment from walnut shells, although I have collected some for the purpose. I did try to make brown using a piece of yellow ochre mineral (iron sulfide and oxide) I had, but the powdered ochre would not mix with water and rubbed off the paper even when I tried using some gum Arabic to bind it.

Beginning to paint the background washes using cobalt blue (which looks pink when wet) and prussian blue.

Beginning to paint the background washes using cobalt blue (which looks pink when wet) and prussian blue.

As explained above, red is a problem. I didn’t want to make red using lead or mercury compounds (minium or vermilion) and I couldn’t afford the cadmium, so the last result was to use cochineal, which I ordered from the Dharma Trading Company. Our first attempt was only partially successful. We ground up the insect bodies in a mortar and pestle and a red fluid came out, mostly carminic acid. We tried using it directly as a pigment, but the paint turned black with exposure to air. We then tried adding natural chalk (calcium carbonate) to make a lake, and that started as an opaque burgundy but turned black within a few minutes. Finally, I tried using alum powder (aluminum hydrogen phosphate) as a mordant and it made a nice burgundy color that was permanent.

Adding green robes made from a mixture of lemon yellow with cobalt blue and yellow ochre with Prussian blue.

Adding green robes made from a mixture of lemon yellow with cobalt blue and yellow ochre with Prussian blue.

Further research into cochineal told me that the best way to use cochineal to make carmine pigment is to crush the dried bus in a mortar and pestle, then filter the solid parts out by running the bug juice through filter paper or cheesecloth. Then add alum powder to stabilize the deep burgundy color. By adding a little vinegar, the color can turn a bright transparent red to reddish orange that will stain and dye cloth and work well for a watercolor pigment. I will try adding some chalk to it at this point to make the pigment opaque for pastels or paint.

Flesh tones (lemon yellow with cobalt pink) and gray beard (carbon black).

Flesh tones (lemon yellow with cobalt pink) and gray beard (carbon black).

As for the brown colors, even to this day most browns come from a clay which is dug out of deposits near the towns of Sienna and Umbria in Italy, then ground fine and used as a pigment. Sometimes they are heated or “burnt” to darken the color. This produces the colors raw and burnt sienna and burnt umber. I can’t exactly take a trip to Italy just to dig up dirt, so I’m working on my own browns out of walnut shells and other organic and mineral sources. I’m a bit stumped on how to grind up the walnut shells to get a fine powder.

The finished Democritus with pen and ink details. It was painted entirely with homemade pigments and inks.

The finished Democritus with pen and ink details. It was painted entirely with homemade pigments and inks.

I’ve included some of the paintings we’ve done. I did the one on Democritus, but others were done by students. I added details at the end with iron-gall ink and Prussian blue ink and a Speedball drawing pen. I also have a piece of watercolor paper that I’ve been using to paint and test swatches of our homemade paints, and you can see we’ve had some interesting results. We can now create about any hue, shade, or tint we need.

Paper of color swatches, used to try out variations and mixtures of pigments. The stabilized carmine is the deep burgundy swatches. The bright cyan is cobalt blue.

Paper of color swatches, used to try out variations and mixtures of pigments. The stabilized carmine is the deep burgundy swatches. The bright cyan is cobalt blue.

This has been a fun and informative exercise in inquiry and experimentation. We’ve seen most of the types of chemical reactions, have seen a variety of physical and chemical changes, and have even practiced some stoichiometry as we work on the finding the best ratios of reactants for our pigments.

Sebastian painting Greek armor using Prussian blue and cobalt blue with carbon black pigment he made.

Sebastian painting Greek armor using Prussian blue and cobalt blue with carbon black pigment he made.

Painting of stained glass windows by Nicole.

Painting of stained glass windows by Nicole.

A painting of fireworks in progress.

A painting of fireworks in progress.

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Visualizing electronegativity of the elements in 3D

Visualizing electronegativity of the elements in 3D

While teaching the history and patterns of the periodic table of the elements to my chemistry students, I wanted them to get a better feel for the concept of periodicity – that some elemental properties repeat periodically as you increase atomic numbers.

Melting points of the elements visualized in 3D

Melting points of the elements visualized in 3D

For example, at the left of each period (row) is an element that is a soft metal that will react with water to produce a strong base. As a family they are called the alkali metals, and consist of lithium, sodium, potassium, rubidium, cesium, and francium. We now know they have a similar electron configuration, with a single electron in an s-type orbital. This electron is easily ionized away and accounts for the alkali metals’ high reactivity. Other families of elements (usually found in columns in the table) include the noble gases, the halogens, and the royal metals (copper, silver, and gold). It was the relationships of similar properties that led Mendelyev (and de Chancourtois, Newlands, Oddling, and Meyer) to develop the periodic table in the first place.

Melting points with a golden texture

Melting points with a golden texture

In an effort to visualize these patterns more clearly, I have devised a technique for taking the numerical values of a property, such as electronegativity, atomic radius, or melting point and turning them into three-dimensional models.

Chart for recording the numerical values of a periodic property

Chart for recording the numerical values of a periodic property

I start with a chart that is divided into squares in the shape of the periodic table, with white squares representing elements and black squares the spaces between and around the sections of the table (you can download this diagram here).

Periodic Properties Chart: 3D periodic properties table

Pairs of students look up one of the periodic properties, then write the numbers down for each element on the chart.

In a text editing program such as Text Edit or Microsoft Word, my students then type in the numbers for each row of the chart, separating them by commas and hitting return or enter to make the next row. For the black squares, they type in a zero. They have to be careful not to leave any element or blank square out. They will have 12 rows of 20 numbers each.

Electronegativity values typed in as comma-separated rows. Blank spaces on the chart are given zeros. The final grid is 12 rows of 20 values each.

Electronegativity values typed in as comma-separated rows. Blank spaces on the chart are given zeros. The final grid is 12 rows of 20 values each.

Once the comma-separated rows of numbers are done and checked, the students save the array as a raw text file (.txt) so that all formatting is erased. They then load the file up into a program called Image J. This program is freeware developed by the National Institute of Health and is very useful for analyzing images. To load in the number array .txt file, students need to go to the file menu and choose “File-Import-Text Image” and select their .txt file. This will create a grayscale image based on the .txt values: the lowest values (the zeros around the edges of the periodic table) are black and the highest value is made white. It will be a small image since the entire array is 20 by 12 pixels. You can save the image created or zoom in on it as close as it will with Command-+ and save a screen shot of it.

Importing the .txt file as a Text Image into Image J software

Importing the .txt file as a Text Image into Image J software

The original grayscale heightmap is only 20 x 12 pixels. You will need to zoom in and save a screen shot of the image.

The original grayscale heightmap is only 20 x 12 pixels. You will need to zoom in and save a screen shot of the image.

In Adobe Photoshop or GIMP, students load in the screen shot and cut it so only the grayscale area remains, then increase the resolution. You will need to blur it slightly (2-3 pixel Gaussian blur) to get rid of artifacts around the edges of the squares. Then make the canvas square by adding a black background using the “Image-Canvas Size” feature in Photoshop. You can do a similar function in GIMP. Save it as an RGB or 8-bit grayscale PSD or PNG file. This prevents the grayscale heightmap from getting distorted in the 3-D terrain editor.

The grayscale heightmap in Image J after zooming in.

The grayscale heightmap in Image J after zooming in.

Now open up your favorite 3-D modeling software. I use Daz3D Bryce because it makes excellent terrains. Most other 3-D software can do terrains out of grayscale heightmaps. Some free or low cost options are Blender and Autodesk Maya (you can find a free PLE version of it). You will then need to load in the square grayscale file you just made using the “Load” buttons in the Picture tab of the Terrain Editor, smooth it, and put a texture on it.

Electronegativity heightmap after adding black edges to make it a square. This avoids distortion in the 3D modeler.

Electronegativity heightmap after adding black edges to make it a square. This avoids distortion in the 3D modeler.

At this point you have a 3-D terrain showing the strength of a periodic property for each element. I am including several examples here. The models can be animated or have a camera fly around it. You can add lights and render out images, then put together a class powerpoint using all the student’s images to demonstrate periodicity and the Periodic Law.

The Terrain Editor in Daz3D Bryce. The model may need additional smoothing to round off artifacts.

The Terrain Editor in Daz3D Bryce. The model may need additional smoothing to round off artifacts.

I’ve also put together a video that describes the history of the periodic table as narrated by Dr. Eric Scerri of UCLA. You can find it on the video page of this blog.

Electronegativity model in Daz3D Bryce. An altitude sensitive texture has been applied.

Electronegativity model in Daz3D Bryce. An altitude sensitive texture has been applied.

Give it this activity a try and let me know how it turns out. I’d love to see examples of what your students come up with.

Electronegativity model in Daz3D Carrara with a little mood lighting

Electronegativity model in Daz3D Carrara with a little mood lighting

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Self portrait of Leonardo da VInci

Self portrait of Leonardo da VInci

Ever wonder where ink comes from, how it was invented and how it is made? I do. Most of the ink we use today for printing newspapers or drawing is called “India” ink (although it was invented in China). It uses carbon black, or soot, for the pigment. But before this ink formula reached Europe, artists and scientists used a type of ink based on iron known as iron-gall ink.

Original drawing by Leonardo da Vinci using iron-gall ink

Original drawing by Leonardo da Vinci using iron-gall ink

In July, 1984, I had the opportunity to travel to Europe with my family. Among many works of Renaissance art, I saw a display of original drawings by Leonardo da Vinci in Florence. There were plans of statues he was commissioned to cast, sketches of human anatomy, and designs for fantastic devices. One thing that caught my eye was his artistic ability; how well he could draw directly using pen and ink. I remember wondering where he got his ink from, which had turned brown with age. Now I know the answer, and I’ve turned it into one of my favorite activities in chemistry.

Alchemical manuscript by Sir Isaac Newton, at the Chemical Heritage Foundation

Alchemical manuscript by Sir Isaac Newton, at the Chemical Heritage Foundation

Iron-gall ink was used for about 1400 years and only lost favor in the mid 1800s when India ink replaced it (because it was cheaper and easier to make and produced a more consistent, longer lasting black). But there’s something to be said for the artistic variety and richness of the shades of iron-gall ink and how it has oxidized with time. The manuscript shown here was written by Sir Isaac Newton with his own homemade ink. It is one page of 24 in the possession of the Chemical Heritage Foundation in Philadelphia and is a series of notes he made on his alchemical experiments (yes, Isaac Newton was an alchemist; in fact, he wrote far more pages on alchemy than he ever did on physics).

Isaac Newton's recipe for iron-gall ink

Isaac Newton’s recipe for iron-gall ink

Newton also left behind his own recipe for ink, as seen here. He started out by collecting galls off of oak trees. These galls are formed when a species of wasp lays an egg in an oak bud, which causes the oak to form a rounded ball or gall around the developing wasp larvae. As Newton’s recipe shows, he soaked the galls in strong ale or beer for a month along with solid gum Arabic. The rotting oak galls would produce tannic acid. The gum Arabic, which comes from the gum of acacia bushes in northern Africa, is used here as a binder to help the ink stick to the paper and keep the pigment in suspension, as well as make the ink have a better flow and consistency. Newton would then mix the tannic acid/gum solution with copperas. This is a chemical with a greenish-blue color that was mistakenly thought to contain copper (hence the name) but is really iron (II) sulfate. The mixture of the iron (II) ions with the tannic acid produced a rich dark brown-black suspension ideal as an ink pigment.

Chemistry students making ink

Chemistry students making ink

The question is how to make similar ink using modern equivalents. I’m not about to soak oak galls in ale for weeks; as it turns out, tannic acid is readily available from strong tea. The iron (II) ions can be produced from steel wool by boiling it in vinegar, filtering the solution through wet filter paper, then adding a small amount of 3% hydrogen peroxide. The trick is to not oxidize the iron too much, or you’ll get too much rust (iron (III) oxide) and your ink will be too brown. Getting a nice black color with just a hint of brown is ideal. If the ink is too thin, then it can be left out to evaporate and make it more viscous. A few drops of gum Arabic are added at the end. You can buy gum Arabic in most craft or art supply stores. If you add too much, the ink will be too glossy when it dries. I originally came across this procedure in ChemMatters magazine (“An Iron-Clad Recipe for Ancient Ink” ChemMatters, October, 2001) and have tinkered with it over the years.

Chemistry students drawing illustrations with their own homemade ink

Chemistry students drawing illustrations with their own homemade ink

So what is the ideal recipe to make the darkest ink? That’s the inquiry part of this lab. I have the students experiment with different formulations to see what the best ratios of steel wool, vinegar, hydrogen peroxide, and tea would be. They also change the time that the steel wool/vinegar mixture is allowed to boil. They begin by learning the old recipe using oak galls, then learn the modern equivalents. From that, they identify variables to test. These factors (or ingredients or procedures) can be listed on the board and divided into comparison groups. Small groups of 2-3 students are assigned to each possibility, such as one group testing the amount of steel wool and its gauge, another testing the strength and amount of the vinegar (kitchen strength or glacial acetic acid) and how long to cook it, another group can test the hydrogen peroxide amount, and another the strength and amount of the tea to add. All of these results can be compiled and compared to create the ideal recipe for making the darkest ink.

Using a traditional drawing pen with homemade ink

Using a traditional drawing pen with homemade ink

The procedure outlined in the ChemMatters article calls for students to boil 200 mL of water, then soak two tea bags in it for five minutes. Meanwhile, a steel wool pad is placed in a beaker with 100 mL of vinegar and boiled for seven minutes. The solution is filtered and cooled to room temperature, then 1 mL of 3% hydrogen peroxide is added. The grayish solution turns a reddish brown as the some of the iron (II) is converted to iron (III) ions (during our Intersession class, I had students use 10 mL of the hydrogen peroxide by mistake and their ink turned too brown). The iron solution and the tea are both added to small cups or vials in equal amounts and stirred together. A few drops of gum Arabic are added. My experience using this recipe produced rather anemic gray ink. As you can see from the illustration of Cai Lun (the inventor of paper) by Evan, with some experimentation you can achieve a very nice dark ink which compares favorably with India ink.

Cai Lun, the inventor of paper. Notice how rich and dark the ink is.

Cai Lun, the inventor of paper. Notice how rich and dark the ink is.

Of course, what my students have done deliberately in one class period took people during the Middle Ages centuries of trial and error to develop, and even by Newton’s time, everyone still had their own recipe. As you can see from the manuscript page, his was a good formula and made dark brown-black ink that has held up well for almost 400 years.

Zach practices daring Elvish calligraphy using homemade ink

Zach practices daring Elvish calligraphy using homemade ink

Once my students create good ink, they go farther and use traditional drawing pens to create illustrations related to the history of chemistry. They pick a material to research, such as glass or steel or armor or stained glass or paper, write up its history and manufacturing, and create their own illustrations with the iron-gall ink. I am showing some of these in this blog. We’ve tried different formulas. In the Intersession Science and Art class I taught in March, we cooked the steel wool for too long in the vinegar and got too much iron (III) ions, or added too much strong tea. The result was sepia colored ink instead of dark black, as shown in the ladybug drawing.

Illustration of armor by Sebastian using iron-gall ink

Illustration of armor by Sebastian using iron-gall ink

Try it out for yourselves! Make sure to use uncoated steel wool. You can get it easily at a hardware store. The other chemicals are household strength and readily found, except for the gum Arabic. Most art supply stores do have bottles of this. It is a bit pricey but a little bit is all that is needed. Two bottles should be enough for a class of 30 students. You will also need some bottles or phials to store the ink (it will last a long time and can be reconstituted with water if it dries out), drawing pens and Bristol board illustration paper, which will be the largest expense of your lab.

Illustrations from my Intersession class where the iron was overly oxidized and turned a sepia color.

Illustrations from my Intersession class where the iron was overly oxidized and turned a sepia color.

As an initial demonstration and “hook”, I use a traditional quill pen and some parchment paper to show how it used to be done. I also demonstrate writing Chinese characters (tsz) using ink sticks, inkwells, traditional maubi (drawing brushes), and rice paper. I’m not very good at drawing tsz, but at least I can show how to hold a maubi and use ink sticks (which are not iron-gall ink – they are “India” ink based on carbon black bound together in stick form, then rubbed with water in an ink well). The “love” character shown was drawn by Miyuki, a Japanese exchange student, on parchment.

Illustration of plate glass making by Nicole

Illustration of plate glass making by Nicole

Drawing of Aristotle using iron-gall ink. I did this as a demonstration project for the chemistry students.

Drawing of Aristotle using iron-gall ink. I did this as a demonstration project for the chemistry students.

Illustration of Chinese fireworks by Richard, made with iron-gall ink

Illustration of Chinese fireworks by Richard, made with iron-gall ink

Alec's Anime drawing. Behind it are pigments we made for watercolors. Stay tuned for that post!

Alec’s Anime drawing. Behind it are pigments we made for watercolors. Stay tuned for that post!

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