pH and ink colour

[Chris]

I know from many posts that we each see differences in the colour of ink as a result of using different pens (flow rate and line width) and different papers (smoothness, absorbance etc) but I wondered....

 

Many coloured chemicals (such as dyes) can change their colour depending on the pH of the liquid in which they are dissolved (eg litmus, which is red in acidic solutions and blue in basic/alkaline solutions). Given that inks are made or end up with a certain pH, is it possible that any change to the pH of the ink might alter the colour we see?

 

How could that happen? Perhaps even the act of writing allows some material on the surface of the paper to dissolve in the ink as it is laid on the paper, altering the pH and thereby affecting the colour.

 

Or have I been sniffing too much ink?

 

Chris

[Limerick]

I've heard Lamy Black has an acid pH. Once solved in a neutral solution, a yellowish tint becomes visible. Adding some vinegar acid to the solution, the yellowish tint disappears and the ink turns back to black. So maybe there is a dye in the ink that causes the change in colour.

[psfred]

Dyes by their chemical nature are fairly ''charged" molecules and the aniline dyes in particular have several nitrogen atoms in them -- it's the particular configuration of nitrogen and carbon bonds that allows light to be absorbed (and often converted to energy -- quite a few dyes fluoresce, that is absorb light at one wavelength and emit it at another).

 

The presence of the nitrogen atoms (and other atoms as well, like oxygen and sulfur) cause the molecules to have partial charges, and this makes them sensitive to the pH of the solution, pH being a measure of the hydrogen (positive ion of hydrogen, or really a naked proton) content of water. With changes in the hydrogen ion concentration, the charge on the dye molecule can change, and this will often change the color. It can also greatly alter the solubility of the dye, so some dyes must be in a solution of a particular pH, else they won't dissolve or poorly dissolve. This is particular to each different dye, and the older aniline dyes were quite often only really soluble and useable as ink in fairly acidic solutions. Some of the metallic dyes are much more soluble, or of the correct color, in alkaline solution (think Superchrome ink).

 

As dye science as progressed, more and more neutral dyes suitable for use as fountain pen ink have become available. This is mostly as a result of research for things like textile dye, of course, as fountain pen ink isn't much of a market driver, no matter how much WE are excited about it, the amount used is infinitesimal compared to the amount of dye used in printing or cloth manufacture.

 

Modern inks are much more likely to be neutral pH as a result, including old "standbys" like Quink and Skrip. Skrip in particular was totally reformulated when manufacture was moved to Slovenia, and the colors are hence different. Not a huge change, but visible. However, I suspect the inks are better for the change.

 

Pelikan Royal Blue seems to be an old formula, it's rather acidic, as is any iron-gall ink, by it's very nature.

 

The pH effect probably explains some of the ink color changes I've seen discussed here, along with the fact that some inks can be "discharged" (as the dyeing industry calls controlled removal without bleach) by sulfites -- acid paper is high is sulfites, and that will cause some inks, mostly blue inks, to fade.

 

Hope that explains things a bit.

 

Peter

Edited May 10, 2008 by psfred

[chuancao]

Dyes by their chemical nature are fairly ''charged" molecules and the aniline dyes in particular have several nitrogen atoms in them -- it's the particular configuration of nitrogen and carbon bonds that allows light to be absorbed (and often converted to energy -- quite a few dyes fluoresce, that is absorb light at one wavelength and emit it at another).

 

The presence of the nitrogen atoms (and other atoms as well, like oxygen and sulfur) cause the molecules to have partial charges, and this makes them sensitive to the pH of the solution, pH being a measure of the hydrogen (positive ion of hydrogen, or really a naked proton) content of water. With changes in the hydrogen ion concentration, the charge on the dye molecule can change, and this will often change the color. It can also greatly alter the solubility of the dye, so some dyes must be in a solution of a particular pH, else they won't dissolve or poorly dissolve. This is particular to each different dye, and the older aniline dyes were quite often only really soluble and useable as ink in fairly acidic solutions. Some of the metallic dyes are much more soluble, or of the correct color, in alkaline solution (think Superchrome ink).

 

As dye science as progressed, more and more neutral dyes suitable for use as fountain pen ink have become available. This is mostly as a result of research for things like textile dye, of course, as fountain pen ink isn't much of a market driver, no matter how much WE are excited about it, the amount used is infinitesimal compared to the amount of dye used in printing or cloth manufacture.

 

Modern inks are much more likely to be neutral pH as a result, including old "standbys" like Quink and Skrip. Skrip on particular was totally reformulated when manufacture was moved to Slovenia, and the colors are hence different. Not a huge change, but visible. However, I suspect the inks are better for the change.

 

Pelikan Royal Blue seems to be an old formula, it's rather acidic, as is any iron-gall ink, by it's very nature.

 

The pH effect probably explains some of the ink color changes I've seen discussed here, along with the fact that some inks can be "discharged" (as the dyeing industry calls controlled removal without bleach) by sulfites -- acid paper is high is sulfites, and that will cause some inks, mostly blue inks, to fade.

 

Hope that explains things a bit.

 

Peter

 

 

I was on marcuslink.com and saw a chart. Noticed that most of the ink were acidic. To my surprise, Waterman had a level of around 3 and Pelikan Blue Black was highly acidic at 2.2!! It made me worried but I did some more research and was told that most modern pens have excellent plating and that even some steel nibs like the Phileas can withstand that kind of acidity level. Hope that helps.