An Introduction to Ink
Linseed oil based inks for letterpress, to be specific. You can find suppliers in our directory, Where Can I Find... Ink.
Printing ink is funny stuff, so odd in some aspects of its physics that a special set of rules had to be developed called Rheology, the flow of stiff liquids. But never mind all that stuff, its no help to the amateur printer.
Best is to have a brief look at how its made (or was in the 1950s) and then how it works, with apologies to any professional ink-maker who might stumble on this.
Many commercial inks nowadays, though not all, have vehicles based on a rubber or wax compound, which would have problems for amateur users. They would not be very mixable with traditional linseed oil based colours for example. Commercial ink ranges often have attractive fluorescent, pearlescent and other fancy effects, but careful tests on the job paper would be needed by any amateur. Inks for big printers will sometimes be for exotic drying systems and be totally unusable by amateurs.
How it used to be made, and perhaps some still is…
Imagine having a bag of flour and a tin of stiff treacle and being asked to get every single micron of flour to have a little treacle jacket! That's about the starting point, something of a fine powder – the colour – something soot-like for black, and a very stiff ‘varnish’ (boiled linseed oil).
They get rolled for hours and hours in a sort of three roll mangle. The stiff lump that gradually develops is sheared endlessly and gradually the particles of pigment get separated and coated with the varnish. Some thinner, runnier varnish is added to help the particles get separated. All this takes a long long time, sometimes days.
Old tins from the trade will have skin, like old tins of paint (paint is a close relative of printing ink) but underneath will often be usable stuff. This may need a trifle of a weak/runny boiled linseed oil (which the trade used to call varnish and which Lawrences sell as Copperplate Oil) to be worked in before use. There may also be a need for just a drop of accelerant driers, most of the original having ended up in the skin layer. A disc of polythene or cooking foil will slow down re-skinning. See Lawrences catalogue for driers and for various runny and stiff linseed oils aka ‘varnishes’.
The resultant product is miles too stiff for printing press rollers, so a solvent is added – a solvent that will evaporate in air pretty quickly. So now you have something that will spread on your ink disc and go round the rollers. The ink maker will also add drying accelerant, sometimes not quite enough, and if to go into tins there you are, if into tubes make a shade runnier first.
The resultant ink dries for you on your paper three ways, one by the solvent component flashing off into the air, two by the 'varnish' pigment carrying vehicle component being absorbed by your paper a little, and finally (and slowest) by the drying accelerant making the varnish dry hard by grabbing oxygen from the air. This last may take all night, or even longer. Before this hard dry stage you can only handle the printed sheets with extreme care, preferably not at all.
The proper letterpress ink you get from, say, Messrs Lawrences (Their Linseed range) is fully finished, with fully dispersed pigment. However, old stock oddments you might get from a commercial printer (and old litho ink will often do very well) is commonly not fully ‘finished’, that process was due to be completed on the stacks of rollers on modern giant presses. The ink makers did not tell the printers about this, and very few indeed know. Such acquisitions would need to be worked out on a slab with a palette knife a good deal before the amateur could use it. Out if the tin it will seem a tiny bit ‘gritty’.
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