Hundreds of recipes for iron gall ink have been published over the centuries. The sheer variety and number of these recipes testify to the widespread use of iron gall ink and its primary importance to our literary and artistic traditions. Artists and scribes, domestics and entrepreneurs ­ each concocted their own formula to suit their particular needs.

Interest in making historic inks has increased in the last several years, due in large part to the efforts of a few ink enthusiasts who have shared their vast knowledge and experience on the subject. This website is an effort to continue this dialogue, by sharing information about iron gall ink and promoting an appreciation for its unique place in history.

It is surprisingly easy to make iron gall ink - the earliest recipes are often the simplest - and the ingredients are inexpensive and readily available.

Ingredients

Iron gall ink is essentially created by the chemical reaction between tannic acid and iron(II) sulfate in an aqueous solution. The primary active components in tannin are gallotannic and gallic acid. With iron(II) sulfate, these tannic acids produce a black pigment, called ferrogallotannate or ferrotannate, upon exposure to oxygen. A small amount of pigment forms by reacting with oxygen in the water, but much more pigment is produced after the ink has been applied to paper and exposed to air for several days.

Even though iron gall ink has been highly prized for centuries for its durability and rich color, it is known to be chemically unstable, and may, over time, change color or damage the paper on which it is applied (visit ink corrosion for more information). Recent research indicates that a 3:1 ratio of gallotannic acid to iron sulfate produces the most stable inks.

Although tannic acid and iron sulfate in water will produce a colored solution, it is not a true ink until a water-soluble binder, such as gum arabic, is added to improve the body and flow of the solution so it may be used with quill, reed or steel dip pens (because of the corrosive nature of the ink, it is not recommended for use in expensive fountain pens). Other ingredients can be added to strengthen or change the color of the ink, act as a preservative, or prevent it from freezing. A brief description of the source and function of each ingredient may inspire you to experiment with your own ink formulas.

1. Tannic acid
2. Iron (II) sulfate
3. Water or wine
4. Gum arabic
5. Logwood

1. Tannic acid
Tannic acid is contained in the galls, bark, leaves, roots and fruits of various plants. The greatest concentration of gallotannic acid is found in galls; the bulbous growths formed on the leaves and twigs of trees in response to attack by parasites. Galls are collected from oak, oak-apple and pistachio trees. Depending on the source, they can be amorphous in shape (Japanese and Chinese galls); large, smooth and globular (British and American oak galls); or small, round and spiky (Aleppo galls). Aleppo galls, collected from trees native to Turkey, contain the highest amount of gallotannate, and were used in trial preparations of the inks described below. A lower proportion of gallotannic acid may be extracted from the bark of various trees, including oak, chestnut, mountain ash and cherry.

Various other sources for tannin include pomegranate rinds, horse chestnuts, hemlock and pine bark. However, the active tannins in these materials are different, and the ink will be less durable and have a green tone instead of the blue black color characteristic of high-quality iron gall ink.

Essentially, there are three methods by which gallotannate is extracted from galls. "Instant" ink recipes call for powdered or crushed galls to be mixed with water or other liquid. Others require that the galls be boiled for several hours to release the tannins. The most time-consuming preparations involve fermentation of the galls by mold.

The fermentation process generally produces the richest, blackest inks. As the mold enzymatically digests the gallotannic acid, the solution is transformed to gallic acid. Gallic acid will produce a purer black color in reaction with iron sulfate, while gallotannic acid will produce a comparatively browner pigment. Should you want to make a gallic acid ink without investing the time, pure gallic acid can also be obtained from a chemical supplier.

2. Iron (II) sulfate
Iron sulfate has been called by many different names, including ferrous sulfate, vitriol, and copperas to name just a few. The term "copperas" may be particularly confusing to contemporary readers. Artist manuals distinguish iron sulfate as green copperas and copper sulfate as blue copperas. In early recipes, iron sulfate and copper sulfate were used interchangeably, in part because natural sources of the minerals were usually mined together. As iron sulfate became available through chemical suppliers, some recipes suggested cooking in a copper pot or otherwise adding copper salt to the mixture, presumably based on the belief that copper sulfate reacted with iron sulfate to produce color. However, recent research (currently unpublished) indicates that copper sulfate does not play a significant role in the ink color, and in fact, may inhibit production of the black pigment.

Pure iron sulfate may be obtained from chemical, specialty art or fabric dye suppliers in the form of a pale green powder or granules. A less pure form may be made at home by dissolving iron scraps or nails in a weak acid. However, making your own iron sulfate should never be attempted without a good understanding of the health and safety hazards involved, which is not within the scope of this website. For a more detailed description of the preparation of iron sulfate refer to Manuscript Inks by Jack C. Thompson, available through his website address listed in the links option.

3. Water or wine
Most inks are made in water. Of course, the purity of water varies widely, and older recipes often suggest using rain water, probably because it was thought to be purer than available standing water sources. Water from the tap may be contaminated with chlorine, metals from pipes, calcium and other salts. For this reason it is generally better to use fresh rain water or distilled water instead. In trial preparations of the inks described in this website, only distilled water was used. When measuring the amount of water specified by weight in a recipe, it is helpful to know that one milliliter is approximately equal to one gram.

Wine, beer or vinegar were sometimes used instead of water for the same reason‹ because it was thought to be a purer liquid. Alcohol may also have prevented the ink from freezing in winter, but, since some recipes require boiling the alcohol (which would cause it to evaporate), there may be another explanation for its use. It may be that the glycerin in alcohol increases the rate of extraction for tannin. Alcohol also reduces the surface tension of the ink solution, allowing it to soak more quickly into the paper fibers. Anecdotal evidence suggests that a large proportion of alcohol or vinegar may have a preservative effect, inhibiting mold from growing on the finished ink.

In many recipes, vinegar is suggested as a diluent in place of water to avoid diminishing the intensity of the ink color. Simple tests indicate that, in fact, color is not reduced by the addition of water any more than by vinegar; however, the gloss (imparted by gum arabic) is reduced more in water than in vinegar.

4. Gum arabic
Gum arabic is a water soluble golden-colored sap collected from Acacia trees native to North Africa. It may be purchased from art supply stores in the form of a liquid, a powder or as dried clumps or fragments. Gum arabic keeps the black pigment suspended in the liquid; otherwise, it would settle to the bottom of the container over time. It also helps to thicken the ink, allowing it to flow more easily from the pen or brush onto the paper.

More importantly, the gum holds the ink at the surface of the paper for a few extra seconds before sinking into the fibers. This influences the appearance and durability of marks made with the ink. The ink line is clearer and sharper than it would be without a binding agent, in part because the ink sinks less deeply into the paper fibers. However, too much gum arabic will cause the dried ink to become inflexible, and it can crack and flake off the surface.

5. Logwood
Because the pigment in iron gall ink does not completely form until it is exposed to air, it is not very dark when applied to paper immediately after preparation. To bypass this latent reaction, provisional colorants were often added to the ink to obtain a dark color as soon as it flowed from the pen. Natural dyestuffs, including logwood, indigo, and Brazilwood were used until synthetic aniline dyes replaced them in the late 19th century. Indigo had the further advantage of imparting a preservative effect to the ink.

Logwood has been used as a colorant since at least the Middle Ages, and was used widely in ink formulations produced in the first half of the 19th century. It is obtained from the wood of the campeachy tree and supplied as shavings or splinters by suppliers of artists' materials or fabric dyes. Boiled in tap water, logwood creates a blood red solution, although it will shift to blue in alkaline solutions and to yellow-orange in highly acidic solutions. Unfortunately, the colorant is not very lightfast, and, unlike the iron gall pigment, it will remain soluble in water after drying.

For questions or comments, please contact:
Cyntia Karnes
Conservation Division LM-G38
Library of Congress
101 Independence Avenue, S.E.
Washington DC 20540
Tel. (202)707-5838
Fax. (202)707-1525
Email: ckarnes@loc.gov