Inks: Report on the pH of More than 60 Inks

(This page revised October 23, 2016)

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This article is the work of John Smith. My contribution is editorial: rearranging the material, augmenting it slightly for improved clarity to the lay person, and rewriting for stylistic consistency with the rest of this site.

A question that is on the mind of every inkophile who ever lived is “Will this new ink, the one with a color to die for, eat my favorite pen?” The answer is maybe. How acidic or alkaline an ink is (its pH), although this is not the only factor in how corrosive an ink will be, can affect how friendly that ink is to various pens.

Although we often speak casually about pH in various walks of life, pH is actually a complex scientific subject. Moreover, measuring pH accurately requires some fairly expensive equipment and a thorough understanding of how to use that equipment properly.

To the chemist, pH is defined as the decimal logarithm of the reciprocal of the hydrogen ion activity, aH⁺, in a solution. Stated more simply, it is a measure of the acidity or alkalinity of the solution. pH is measured on a scale from 0 to 14, with 7.0, the pH of pure distilled water, being neutral. The lower the pH, the more acid the solution is; conversely, the higher the pH, the more alkaline the solution is. An alkaline substance is referred to as a base.

The task of measuring pH is far removed from taking a temperature reading or from taking a simple electrical measurement with a voltmeter or ammeter. A pH meter, and more particularly the electrode it uses, is a little miracle of complex science and engineering. Many user-generated errors can operate to make a reading unreliable. As a result, unless the source is known, your first reaction to any reported pH reading should be a sensible suspicion. I trust John Smith, who ran the tests that are reported in this article; and I trust his equipment and his methodology, both of which are described below.

Apart from user-generated errors, many factors can be regarded as contributing to variations between readings from different sources. The following list describes three such factors:

• All pH readings are temperature dependent; thus, a pH reading can only be expressed accurately in the form “x pH at y temperature.”

• Over time, natural chemical reactions within a bottle of ink can alter the pH of the ink, especially once the bottle has been opened and carbon dioxide has entered.

• Not all batches of the same ink are necessarily identical. This is especially important to note in light of the fact that some ink manufacturers introduce slight formulaic variations periodically to aid law enforcement in the forensic analysis of writing samples.

The Equipment

The apparatus used was an SI Analytics Lab 870 benchtop pH meter coupled with a virtually new SI Analytics BlueLine pH 15 all-glass electrode that was fully pressurized before the tests. It has an integrated negative temperature coefficient (NTC) temperature sensor. This is a sophisticated, laboratory quality pH meter with Stability Control, automatic buffer-set recognition, electrode diagnostics, and full spectrum error reporting.

The Methodology

The instrument was calibrated to two points using fresh Schott DIN Technical calibration fluids at pH 7.0 and 4.01 at 25° C (77° F).

All readings were established using the instrument’s Stability Control. Using Stability Control allows the instrument, not the user, to determine when the reading is optimal and stable. In this way, accuracy and reproducibility of readings in chemically complex solutions is greatly enhanced.

During the testing, the calibration was regularly checked against the buffer solutions, and no drift was detected. Standard laboratory practices were followed throughout the testing, and a random selection of inks was retested the following day.

At the time of the tests, none of the inks tested had been open for more than 18 months.

Note While pH is an important factor in the safety of a given ink, it is not the only criterion. There are other factors to consider, such as the ink’s tendency to clog, its ability to lubricate well, and whether it stains and/or damages pens and other surfaces. For more information about inks and their behavior, read Inks: The Good, The Bad, and the Ugly.

The Results

In the following table, results are listed from lowest pH (most acidic) to highest (most alkaline/basic). As a basis for comparison, distilled white vinegar, a weak acid, usually has a pH of about 2.4 at the standard strength of 5%. Chlorine bleach, a weak base, has a pH of about 11.

Manufacturer	Ink	Color	pH at 22° C (71.6° F)
Rohrer & Klingner	Salix		1.53
Rohrer & Klingner	Scabiosa		1.73
Rohrer & Klingner	Magenta		1.99
Rohrer & Klingner	Königsblau		2.09
Pelikan	Turquoise		2.30
J. Herbin	Bleu Myosotis		2.31
Diamine	Blue Velvet		2.42
Rohrer & Klingner	Leipziger Schwarz		2.42
Diamine	Red Dragon		2.48
Montblanc	Royal Blue		2.57
Private Reserve	Electric DC Blue		2.65
Diamine	Sargasso Sea		2.66
Waterman	Tender Purple		2.69
Diamine	Asa Blue		2.71
Cross	Blue		2.85
Diamine	Royal Blue		2.93
Yard-O-Led	Blue		2.97
ST Dupont	Royal Blue		3.38
Parker	Quink Blue-Black		3.40
Diamine	Majestic Blue		3.52
Pelikan	Violet		3.76
Diamine	Purple Pazzaz		3.83
Diamine	Eau de Nil		4.09
Waterman	Absolute Brown		4.50
Pelikan	Edelstein Sapphire		4.51
Noodler’s	Baystate Blue		4.53
Diamine	Delamere Green		4.59
J. Herbin	Rose Cyclamen		4.67
J. Herbin	Emerald of Chivor		4.69
Visconti	Blue		4.92
Private Reserve	Tanzanite		5.32
J. Herbin	Bleu Océan		5.65
Diamine	Autumn Oak		5.75
Private Reserve	Blue Suede		6.02
J. Herbin	Ivy Green		6.03
Diamine	Syrah		6.04
J. Herbin	Violette Pensée		6.20
J. Herbin	Amber		6.28
Diamine	Burnt Sienna		6.58
Private Reserve	Black Cherry		6.59
Rohrer & Klingner	Cassia		6.73
Rohrer & Klingner	Alt Goldgrün		6.73
Pelikan	Edelstein Amethyst		6.81
J. Herbin	Vert Empire		6.96
Neutral Point, Ph 7.00
Diamine	Ancient Copper		7.06
Diamine	Wild Strawberry		7.16
J. Herbin	1670 Rouge Hématite		7.35
J. Herbin	Poussière de Lune		7.55
Lamy	Black		7.55
Diamine	Pumpkin		7.64
J. Herbin	Lie de Thé		7.66
Pilot	Namiki Blue		7.73
Rohrer & Klingner	Verdigris		7.98
Noodler’s	Apache Sunset		8.40
Pilot	Iroshizuku Take-Sumi		8.56
Sailor	Sei-Boku		8.61
Pilot	Iroshizuku Yu-Yake		8.74
Pilot	Iroshizuku Shin-Kai		9.39
J. Herbin	Rouge Caroubier		9.42
Pilot	Iroshizuku Yama-Budo		9.47
Pilot	Iroshizuku Asa-Gao		9.60
Rohrer & Klingner	Morinda		9.76

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