Logic puzzle articles

Pencil Hardness/Softness Ratings

Monday, September 23, 2002 This piece of raw graphite comes from the Bogala Mine in Sri Lanka, and it is quite pure.

Early pencils were made using cut pieces of raw graphite dug from the earth. The hardness or softness of these pencils was dependent on the quality or purity of the graphite, and so was difficult - or impossible - to control. Different methods of refining and mixing of graphite were experimented with over the years, but it was not until about 1795 that a Frenchman, Nicolas-Jacques Conté, developed a process for making pencil leads that is still in use today.

A 'soapy' feel

The above piece of raw graphite comes from the Bogala Mine in Sri Lanka, and it is quite pure. The photo is an accurate representation of its appearance, ie. it has a silvery-gray color rather than being solid black. I had the privilege of handling this sample; it has a 'soapy' feel to it. Photo by Doug Martin, Courtesy of Dr. John Farver, Dept. of Geology, Bowling Green State University

The process, known as the Conté Process, involves the mixing of finely powdered graphite with finely ground clay particles and shaping and baking the mixture. By controlling the ratio of clay to graphite, varying degrees of hardness can be obtained, as well as fairly consistent and reproducible quality from batch to batch.

The early Conté pencils were made in at least four grades, and a numerical grading designation was used to distinguish them - 1 being the hardest, 4 being the softest. As the Conté process became known and used by other pencil makers, similar grading systems were used by them as well. However, these grading systems were arbitrary and inconsistent from one pencil maker to another.

In the early nineteenth century, English pencil makers began using a letter designation for varying hardnesses. Softer leads were designated with 'B' (for black), harder leads with 'H' (for hard). Different schemes were used to expand the range of grades, such as 'BB' and 'BBB' for successively softer leads, and 'HH' and 'HHH' for successively harder leads.

Standard for pencil grades has ever been adopted

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By the beginning of the twentieth century, a combination letter-number system had been established and was in use by nearly all European pencil makers, and was also used for some American-made pencils. This system is still in use today, and provides for a wide range of grades, usually consisting of the series:

9H, 8H, ... , 2H, H, F, HB, B, 2B, ... , 8B, 9B where 9H is the hardest, 9B is the softest. At the same time, a number-only system was in use, particulary in the U.S., which is still in use. The table below indicates approximate equivalents between the two systems: #1 --- B, #2 --- HB, #2½ --- F, #3 --- H, #4 --- 2H

The common #2, or HB grade pencil in the middle of the range, is considered to be the preferred grade for general purpose writing. Harder pencils are most often used for drafting purposes, while softer grades are usually preferred by artists.

American-made pencils can often be found with numerically equivalent designations of 2-1/2, 2-4/8, 2-5/10, and 2.5, representing the same grade, but introduced by different manufacturers to distinguish their products and to avoid patent lawsuits.

It should be noted that no 'official' standard for pencil grades has ever been adopted, and the designations are still somewhat arbitrary and not always consistent from one manufacturer to the next.

Reprinted with permission

Originally published in pencilpages.com , November 3, 1997