Ancient inks

Student Sheet

In this practical I will be:

• Learning and using key terms, such as, suspension, reaction, pigment, opacity and tack.
• Creating and using my own ink.
• Evaluating the effects of various factors on: the ease of use; opacity; drying time and pH of my ink.

Introduction:

You have finished a piece of art you were commissioned to create. Unfortunately, as you live in ancient times, mobile phones have not been invented yet. Therefore you will need to write a letter to your patron, informing them that their art is ready for collection.

Your bad luck continues as you have just used up the last of your ink! Luckily, as a science-artist, you can make some more…

Equipment:

• 90 g of dry oak galls

• 400 cm3 of water

• 60 g of iron(II) sulfate, 

• 30 g of gum arabic 

• 2 mouth masks

• 1 mortar and pestle

• 1 beaker (600 cm³)

• 1 measuring cylinder (500 cm³)

• 1 sheet of card to cover the 600 cm³ beaker top

• 1 sheet of coarse filter paper

• 1 stirring rod

• 1 pen and pen nib

• 1 sheet of white paper

Alternatively, if using tealeaves

Equipment:

• Dry black tealeaves (could be labelled as ‘Oak Galls substitute’)

• Pestle and mortar

• 1 beaker (250 cm³)

• 1 beaker (100 cm³)

• Stirring rod

• 1 measuring cylinder (100 cm³)

• Distilled water

• Iron(II) sulfate (HARMFUL and IRRITANT)

• Gum arabic (or craft glue)

• Plastic pipette

• Spatula

• Weighing boat

• Watch glass (or cover for the beaker)

• Filter paper

• Filter funnel

• 1 conical flask (100 cm³) 

• Universal indicator paper and colour chart

Access to:

• Straws
• Scissors
• A4 paper
• Digital balance
• Paper towelling
• Disposable gloves
• Blotting paper
• Hot water
• Wear safety glasses. Wear disposable gloves.

Method:

Wear safety glasses. Wear disposable gloves.

1. In advance: Make sure the galls are very dry so leave them in a warm dry place for 24 hours.
2. Wearing a mouth mask; break the galls into pieces, then grind them with a pestle in a mortar or use a coffee mill to form a fine powder of the galls.
3. Transfer the gall powder to a 600 cm³ beaker.
4. Measure the 400 cm³ of water in a measuring cylinder; add the water to the ground galls. Cover with a card top and leave the mixture to ferment in a sunny corner at room temperature for 3 days.
5. Using a coarse filter paper filter the mixture and add the iron(II) sulfate to the solution. Stir well and leave for another 3 days.
6. Add the gum arabic crystals; stir the mixture to form your ink. 
7. Now test the ink using a pen nib.

Alternative method if using tealeaves:

1. Place the tealeaves into the pestle and mortar and grind them to a powder.
2. Put this powder into a 250 cm³ beaker.
3. Use the measuring cylinder to measure 50 cm³ of hot water and add the water to the powder in the beaker. Stir, then cover and leave to cool for 10 minutes.
4. After ten minutes, stir again before using the filter paper and funnel to filter the solution into a conical flask. 
5. Rinse the beaker so it’s ready to use again. The powder and filter paper can now be disposed of in a bin. 
6. Pour the solution from the conical flask into the 250 cm³ beaker.
7. Carefully weigh 6 g of iron(II) sulfate and add this to the solution in the beaker. 
8. Stir to dissolve the iron(II) sulfate and mix it into the solution.
9. Add a plastic pipette full (or two teaspoons) of gum arabic liquid to the solution in the beaker and stir the mixture again to form the ink. Pour the solution back into the conical flask.
10. Use the scissors to make a diagonal cut on one end of a straw to form a nib so that you can use the straw to write with.
11. Now test the ink using your pen (straw).
    • Why do you think the galls need to be dry?
    • Why do you think the galls are ground to a fine powder?
    • What is fermentation?
    • Test the pH of the ink. Is it acid or alkali?
    • Why would the pH be important for the long time use of the ink?

Going further:

Keep your writing samples and examine them after several days. Did their appearances change? If so, what do you think caused the changes?

Find illustrations in art books showing drawings made by Leonardo da Vinci and describe the appearance of the lines he drew with iron–gall ink. How does iron(III) tannate pigment change over long periods? How would you explain this colour?

Theory:

Explanation appropriate for KS4

Tannic acid is a complex organic compound naturally found in bark, fruits, nuts, leaves, and insect galls. There are several forms of the acid, and it is known as tannin, gallotannin, gallotannic acid, and coriligan. Hence the chemistry of making ink is a complex one but a simplified explanation follows.

When the powdered galls are added to water and left to ferment two reactions occur:

• the fermentation of gallotannic acid to gallic acid by the enzyme tannase;
• followed by the formation of the ink pigment by the addition of the iron(II) sulfate.

The ink is very acidic and that acidic nature, over the centuries, makes the ink fade, discolour and damage the paper.

Explanation appropriate for KS5

The iron-gall ink pigment is made from gallic acid. However galls contain large amounts of gallotannic acid and relatively little gallic acid so the galls are fermented. During the fermentation the fungi Aspergillus niger and Penicillium glaucum, found in the galls, release the enzyme tannase which, over three days, catalyses the hydrolysis of gallotannic acid to form gallic acid and glucose.

When the iron(II) sulfate is added an acid-base reaction takes place followed by a redox reaction. Gallic acid and iron (II) sulfate form iron(II) gallate (a colourless water-soluble compound), H3O+ and SO42−. Then, almost immediately, the iron(II) gallate reacts with atmospheric and dissolved oxygen to produce water and iron(III) pyrogallate.

Iron(III) pyrogallate is a black insoluble octahedral complex in which the ligands of each Fe3+ cation are two molecules of gallic acid. The presence of the H3O+ ions makes the solution acidic.

The acidic nature has, over the centuries, made the ink fade, discolour and damage the paper. There is an excess of Fe2+ ions. The 2:3 ratio of iron(II) sulfate to galls means there is more iron(II) sulfate than is necessary to react with the gallic acid and some of these surplus cations oxidise to form Fe3+ oxide which, as it is paler than iron(III) pyrogallate, fades the original black colour of the ink. 

This method is based upon the article in Issue 6 Science in School Galls which can be found here. 

Teacher and Technician Sheet

In this practical students will:

• Learn and use key terms, such as, suspension, reaction, pigment, opacity and tack.
• Create and use their own inks.
• Evaluate the effects of various factors on: the ease of use; opacity; drying time and pH of their inks.

Please note: this experiment will take at least 7 days to complete.

Introduction: 

(The topic could start with a group discussion during which teachers introduce the following ideas, especially the words in bold. It is important to realise this practical takes at least 7 days to complete so might be worth considering as a demonstration or for use in a science club setting.)

We all use ink nowadays mostly in the form of a ballpoint pen. In times past, the user would dip a stick or feather with a nib cut or stuck on it into an ink and write. There are medieval (5th to 15th century) miniatures showing the Devil attempting to steal precious ink from St. John of Patmos. These demonstrate the importance of ink to the monks.

During the medieval period, two kinds of ink were used. The earliest ink, from around 2500 BCE, was black carbon ink. This was a suspension of carbon, water and gum. Later, from around 3rd century CE, brown iron-gall ink was used. This was obtained from oak galls. Gum arabic is added to keep the insoluble solids in suspension.

The reaction that produced the ink was known about in Roman times. The Roman writer Pliny the Elder (23–79 CE) described in his Naturalis Historia (Natural History), an experiment describing how to distinguish verdigris, copper(II) ethanoate [Cu(CH3COO)2.2Cu(OH)2], used to process leather, from the cheaper copperas, iron(II) sulfate (FeSO4.7H2O) with which it was often adulterated.

Pliny did not know the chemistry of the reaction but, he described the process so chemists can recognise the reaction. Chemists now know the reaction between the iron(II) cation (ferrous) and gallotannic acid found in iron-gall ink. Analysis of the Dead Sea Scrolls ink has shown evidence of iron-gall ink so although it was not a common ink until 200 CE the ink material had been used.

Modern ink is more complicated. It contains many ingredients. The coloured substance is the pigment and the liquid is known as the ’vehicle’. These include substances that keep the acidity around neutral, known as pH modifiers. There are humectants that slow down the drying, resins to help binding and flow, defoamer/antifoaming agents to control the foaming of the ink, wetting agents to control surface properties, biocides to stop the growth of fungi and bacteria, and thickeners to control ink application.

The pigment is what gives the ink its colour and depth known as the opacity. However, when the inks are exposed to long periods of sunlight, especially bright sun, or strong heat the colour of the ink will change over time or fade this is known as the permanence of colour. Another important thing with an ink is the stickiness or flow known as tack. Too sticky and the ink will not flow with the nib onto the paper.

When carbon ink was used on the early parchments it would rub off because the surface is not absorbent, but the addition of gum arabic helped the ink to stick. The later iron-gall ink burnt into the surface by reacting with the collagen in the parchment. This however proved to be a problem because the ink was corrosive and over time burnt through the parchment. Nowadays many libraries have to carry out conservation to save the books.

Carbon ink worked well on papyrus because it is absorbed into the surface of papyrus where it dries and remains. Iron-gall ink when used on papyrus also reacts with the chemicals of the papyrus. This time it is reacting with the cellulose in the papyrus. However, again this reaction of the chemicals in iron-gall with the writing materials is also a problem since it burns the paper.

The iron-gall ink was used by people such as Leonardo da Vinci; Bach; Rembrandt and Van Gogh.

The recipe below is based upon one listed by Pietro Canepario, a Venetian, in his De atramentis cuiuscumque generis (All Kinds of Ink; 1619).

(It is good to get the students to investigate the different types of galls that could be found on trees like the oak or cypress. It is advisable not to mix the different galls then they can investigate the different ink colours and the criteria for the best type of ink such as flow, rate and coverage.)

(This practical can be done with pupils working in groups of two. Groups of two allows for good discussion between the pupils. Teachers can use the questions set as the stimulus for discussion and the answers can be used as a group report, article, presentation, poster or talk.)

Curriculum range:

Suitable for middle and lower secondary schools and if the chemistry is considered upper secondary; it links with:

• asking questions and developing a line of enquiry based on observations of the real world, alongside prior knowledge and experience; 
• using appropriate techniques, apparatus, and materials during fieldwork and laboratory work, paying attention to health and safety; 
• making and recording observations and measurements using a range of methods for different investigations; and evaluating the reliability of methods and suggest possible improvements; 
• presenting observations and data using appropriate methods, including tables and graphs; 
• interpreting observations and data, including identifying patterns and using observations, measurements and data to draw conclusions; 
• presenting reasoned explanations, including explaining data in relation to predictions and hypotheses; 
• the concept of a pure substance; and
• mixtures, including dissolving. 

Hazard warnings:

Iron(II) sulfate is harmful if swallowed (Acute toxin Cat 4, oral) and is a Skin/Eye Irritant (Cat 2)

Iron(II) sulphate solution is IRRITANT 

Wear a mouth mask to prevent breathing in any of the dust of the galls since they can contain fungal spores

The water can be provided hand hot from the tap and should not present a hazard assuming the expected levels of behaviour.

Tannic acid is an eye irritant (Cat 2)

Gum Arabic is generally of low hazard but may be a skin/eye irritant (Cat 2). It may also be a skin/respiratory sensitizer. (Check with the safety data sheet.) This is still the case at the concentration found in the ink – so gloves are sensible.

Equipment:

Wear safety glasses. Wear disposable gloves. 

For a group of 2 students:

• 90 g of dry oak galls 
• 400 cm³ of water
• 60 g of iron(II) sulfate
• 30 g of gum arabic 
• 2 mouth masks
• 1 mortar and pestle
• 1 beaker (600 cm³)
• 1 measuring cylinder (500 cm³)
• 1 sheet of card to cover the 600 cm³ beaker top
• 1 sheet of coarse filter paper
• 1 stirring rod
• 1 pen and pen nib
• 1 sheet of white paper

Alternatively, if using tealeaves instead of oak galls:

• Dry black tealeaves (could be labelled as ‘Oak Galls substitute’)
• Pestle and mortar
• 1 beaker (250 cm³)
• 1 beaker (100 cm³)
• Stirring rod
• 1 measuring cylinder (100 cm³)
• Distilled water
• Iron(II) sulfate (HARMFUL and IRRITANT)
• Gum arabic (or craft glue)
• Plastic pipette
• Spatula
• Weighing boat
• Watch glass (or cover for the beaker)
• Filter paper
• Filter funnel
• 1 conical flask (100 cm³) (if keeping, use a dark glass conical flask with a bung)
• Universal indicator paper and colour chart

Access to:

• Straws
• Scissors
• A4 paper
• Digital balance
• Paper towelling
• Disposable gloves
• Blotting paper
• Hot water

Technical notes:

Tealeaves can be substituted for oak galls for this practical. 

Each group will need the equivalent amount of tealeaves that are contained in two teabags.

Iron(II) sulfate is HARMFUL at 0.9 M or above and .IRRITANT at 0.37 M and above

The solid is HARMFUL but the method above should produce an initial solution that is less than 0.5 M- however this will become more concentrated over the 3 days.

Tannic acid could be used instead of tealeaves, particularly for KS5.

Results:

The ink produced is easy to write with because of the added stabiliser. 

The dark ink visibly deepens in colour within seconds of being on the paper.  

It takes a short amount of time to dry, which could be decreased by using blotting paper, and has not faded in a week of exposure to bright light.

Testing the ink with universal indicator paper shows that it is strongly acidic (pH 2-3).

Students should be able to use the method above within the lesson time and achieve good results.

The hazards are minimal assuming the expected level of behaviour from students.

Going further:

Keep your writing samples and examine them after several days. Did their appearances change? If so, what do you think caused the changes?

Find illustrations in art books showing drawings made by Leonardo da Vinci and describe the appearance of the lines he drew with iron–gall ink. How does iron(III) tannate pigment change over long periods? How would you explain this colour?