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What Happens To Iron Gall Ink When It Oxidizes?


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I wanted to ask the question here before I resorted to doing numerous experiments. A month or two ago I did an activity with my kids, making iron gall ink. The recipe made enough ink to last me a couple of years of heavy writing. I noticed that when I open a new bottle the ink goes on the paper as a grey ink, but quickly oxidized to a dark black. This is what it is supposed to do. But I also noticed that after the bottle had been opened for a while the ink started to go onto the paper more black. It was oxidizing in the bottle.


I'm sure it would always be better to use smaller bottles and use fresher ink, but that would mean planning to have enough bottles and it's too late now.

Does anyone think there would be any degradation to the performance of the ink if it oxidizes in the bottle instead of on the page?


Thank you for your thoughts.





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By mixing tannin with iron sulfate, a water-soluble ferrous tannate complex is formed. Because of its solubility, the ink is able to penetrate the paper surface, making it difficult to erase. When exposed to air, it converts to a ferric tannate, which is a darker pigment. This product is not water-soluble, contributing to its permanence as a writing ink.


The darkening process of the ink is due to the oxidation of the iron ions from ferrous (Fe2+) to ferric (Fe3+) state by atmospheric oxygen. For that reason, the liquid ink needs to be stored in a well-stoppered bottle, and often becomes unusable after a time.



I cleaned out a couple of pocket pens yesterday. Each had a full cartridge's (re)fill of Pelikan 4001 Blue/Black ink in it for the past several months; but while the Pilot's fill was drawn from a bottle I bought from Cult Pens in August 2021, the Moonman's fill was drawn from a bottle that is more than a decade old. The formulation of the retail product may have changed in the intervening years between the two bottles' production dates, but I'm not certain. The older one is much less saturated in terms of colour (i.e. it is mostly grey), and the newer one is relatively more blue, when laid on the page. The older ink leaves a fainter mark on the page after the sheet of paper is soaked, compared with the newer ink.


But even a change in formulation cannot account for the amount of insoluble particles in the older ink. Both pocket pens were close to (but not quite yet) having lost all of the unused ink in them to evaporation, even though both still (barely) wrote. The Pilot was clean after one ultrasonic cleaning cycle and then a pressurised flush with a bulb syringe. The Moonman was still shedding black soot-like particles after the third five-minute cleaning cycle in the ultrasonic cleaning tank (with pressurised flushes in-between). On account of that, I'd say there was a lot of microscopic insoluble particles suspended in the older bottle of ink, that would not only be apt to produce clogging in a fountain pen, but also contribute little to the permanence of the ink marks produced with the old ink, since in that state there is nothing in the liquid part of the ink to bind them to the fibres/substrate; friction from rubbing, or pressurised flushing with water, of the paper surface should be sufficient to dislodge a significant proportion of the insoluble particles deposited.

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Perhaps most fundamental, for me, is that IG inks are _fun_ because they change after you write due to the oxidation.  If you were to let it completely oxidize so that all the iron precipitates out before writing then that fun part is gone.


One of my assumptions about iron gall:  the iron is in solution, and when you write on the paper some of the liquid penetrates the surface, so that when the iron oxidizes out it is in the paper, which probably enhances it's durability.  As opposed to a pigment ink where more of it presumably on the paper.  If you were to let an IG ink oxidize in the bottle so that the iron precipitates out before you write with it, then isn't it a pigment ink at that point?  I realize that I am oversimplifying, as presumably a pigment ink could have the pigment particles small enough that they, too, get embedded into the paper.


There is definitely a common wisdom in the FP community that you don't want the precipitated iron in your pen, as it will clog.  Hence the recommendation to NOT shake the IG bottle before filling: just leave the sludge at the bottom of the bottle in the bottle.  I don't know if this is really true.  I would expect that this is true if the particles are too big, but are they?  If the particles are similar in size to what is in a normal pigment ink, then would it not be safe?  Or if a little bigger, like the size of particles in a shimmer ink, would it not also be safe but perhaps with the caveat of a recommendation to use in a cheaper or easier to clean pen?

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I've use vintage Parker and Sheaffer iron gall inks.  No problems with particulate matter in them.  If the bottle is sealed well and is reasonably full, they tend to hold their color quite well.  Older blue-black Sheaffer inks turned gray.  The Parker permanent Royal Blue retained it's color well.  We're talking inks from the 40s and maybe 50s.  I quit using them when I decided to start using Pelikan Royal blue for my writing and testing pens.


Keep in mind that the ferogalic inks can corrode steel nibs.  I had some Retro 51 nibs that pitted along the underside of the slit, and on the underside where the nib made contact with the feed.  I recommend using the inks only with gold nibs.  But I do appreciate how permanent they are.

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