Exploring

Inherent Vice: Materials

Ink and Pencil

Ink is essentially a liquid in which one of many possible types of pigments or dyes is suspended. Pencils are made from graphite, a form of carbon. In paper-based collections, ink is encountered not just in documents but also in printed items and artworks. Pencil is generally encountered in handwritten documents and drawings.

History

Inks for writing and drawing were probably first made around 2500 BC in Egypt and China. These were made from carbon suspended in water and vegetable gum (hardened sap). Through the centuries, many other inks were developed using berries, plants, and minerals to provide colorants. When synthetic aniline dyes were developed in the mid-19th century, they were soon used in inks. Since that time, a huge variety of ink formulas have been created, most of which are proprietary, and many of which are prone to fading, color changes, and smearing.

Pencil is a stable medium. The process used to make modern pencils was developed and patented in France in 1795. Henry Petroski's The Pencil (see Additional Resources) provides a history of the development of the pencil. Those caring for collections should also be aware of the existence of copying pencils (developed in the late 1870s for use with the letterpress copying process). Markings made with copying pencils can be mistaken for those made with graphite pencils, but in fact the copying pencils contain not just graphite, but also aniline dyes that are water and alcohol soluble.

Deterioration of Ink

Some inks are water soluble, leading to a loss of information if documents become wet.

Carbon-based inks—These are the earliest types of writing ink. Good quality early carbon inks do not discolor with age, but can smudge in high humidity. Poor quality carbon inks may turn a brown color over time.

Iron gall ink—This was the predominant type of writing ink for many centuries. It was used as early as the fifth century and was common from the 12th century well into the 20th century. Iron gall ink is made by mixing tannic acid with an iron salt. Both high acidity within the ink (leading to acid hydrolysis of the paper) and oxidation of excess iron compounds present in the ink make it very damaging to the support (usually paper). In extreme cases the ink actually "eating through" the support. See the Ink Corrosion Web site for more information on iron gall ink.

Colored inks—Colored inks are made using pigments or soluble dyes (see the discussion of colorants in this session). In general, inks made using light-resistant pigments are of better quality. Inks made from soluble dyes (including most of those used in felt-tip markers) are not lightproof and may be water soluble as well.

Traditional printing inks—Traditional inks used to make prints such as intaglio (engraved) prints or lithographs, differ from writing inks in that they are oil-based (more greasy and gelatinous), allowing them to adhere better to the printing surfaces and to perform well with printing equipment. While many of these inks were quite stable, others used fugitive pigments (which fade over time or on exposure to light) and were subject to bleeding. Also, if the ink was poorly manufactured, excess oil sometimes caused staining. Refer to How to Identify Prints [need reference] for an explanation of printing methods. Refer to Bamber Gascoigne's How to Identify Prints (see Additional Resources) for an explanation of printing methods.

Laser and inkjet printing—These were introduced on a large scale in the 1980s and have now become ubiquitous. Laser printing uses carbon inks and involves the same process as electrostatic copying (discussed elsewhere in this session). Black and white laser printing is quite stable. Most general-use inkjet printers use dye-based inks that are not very lightfast and are often water-soluble. See the discussion of digital prints for more information on inkjet printing.

Fax printing—Thermal transfer technology, used for fax printing and other purposes, became common during the 1980s. Printed documents using this technology tend to be very unstable.