Letterpress: Printing the Blue Plate

You will need two small palette knives with springy blades around 150mm long, one with a round end, one a push-knife (with a flat end like a a high-class decorators scraper). Also a small hand-roller, say 75mm wide x 25mm diameter, a flat ink slab 300 x 300mm or larger, turps and cleaning rags-or kitchen roll. Some might prefer to work in rubber gloves.

Most printing ink comes in cans, of a size which many commercial printers use up in one job! Nevertheless, such cans generally have a close-fitting lid-don’t damage it! Inside a fresh can the ink is covered by an ‘airtight’ waxed-paper or plastic disc, carefully peel this back and skim a suitable amount from the surface, using the push-knife without digging down. A blob the size of half a golf-ball is sufficient for several hundred cards or letterheads. Smooth the airtight disc back: be careful to avoid trapping any pockets of air. The airtight disc restricts oxidation to a thin ring of ink around the wall of the can. If you’ve inherited a carelessly used can you’ll waste, not only time, but more ink than you can use, in trying to pick out bits of oxidised ink ‘skin’-hard insoluble chips-well worth avoiding.

Even in warm conditions, ink needs ‘working’ to make it usable. Don’t spread ink beyond a patch the width of your hand-roller but, with the round-end knife, pummel, lift, fold and beat it vigorously. Friction between the granules of pigment and medium will warm and loosen the ink. Test occasionally by lifting the knife until the strand of ink connecting knife to slab breaks; each time you’ll notice the strand lengthen before breaking. When you can draw up a 100 – 150mm strand, the ink is useable-consistency similar to golden syrup — how deliciously un-healthy!

Scrape most of the ink into a blob and push it out of the way to be your reserve. Roll your hand-roller back and forth over the remaining patch of ink, lifting the roller between strokes to ensure all of its circumference is evenly coated. Transfer, with the hand-roller, a coating of ink to the ink-plate or disc of your press and, before clipping in the forme, work the press-rollers to and fro until they and the disc are evenly coated. Clip in the forme and, with grippers, etc. well clear of the type, work the rollers across ink disc and type forme several times without actually fully closing platen to bed. Now press down fully and take a trial pull on the tympan (the card packing on the platen) and examine it carefully.

If the impression is even, but under-impressed and under-inked, the thickness of a sheet of paper or card will improve it. Carefully position lay-gauges and grippers to locate the paper without hitting the type and try a sheet. If still under-inked, add a little more and try another pull; don’t over-ink, build up gradually.

An un-even impression demands local pressure adjustment; weak at the hinge end of the platen requires more tympan packing, weak at the open end requires less. One corner weak, or heavy demands careful adjustment of the pressure screws behind the bed. If individual letters print too strong or too weak, check for and replace worn letters, plane it (again?) on a clean imposing surface and try again.

This guide kindly contributed by John R Smith of the Old Forge Press. Originally appeared in the newsletter of the Oxford Guild of Printers

Ink Additives

White Ink
White Ink (from Flickr)

Commercial printers used a myriad of additional ingredients to make a difference to their inks.  When printers were using a great mass of ink the unit price was very important, and so cheap ink was common.  A survey of commercial printers showed that common additions at one time were —

  • French chalk
  • Paraffin wax
  • Lard
  • Coconut oil
  • Beeswax
  • Lubricating oil

Work was done to reduce the number of additives (known as dopes) to a realistic number.  The list below should cover almost all changes needed to inks —

  • Heavy Varnish
    will stiffen the ink and also make it dry a little quicker
  • Medium Varnish
    will soften the ink, useful for printing on a softer paper
  • Reducer (‘Number 1’ from a commercial supplier)
    this will slow drying but reduces picking: the action of the ink pulling the surface of the paper away from the main body of the paper
  • Supermatting
    this additive will help ink to dry when overprinting on a surface that will not allow ink to be absorbed, like plastic or metal foil
  • Reducer (‘Number 2’ from a commercial supplier)
    This helps ink soak in to the paper

While some printers had a tendency to add dopes to every ink, the recommendation of the experts was clear: ink maker produce inks that should work direct from the can.  Seek advice from your ink manufacturer about what is best for a particular job and paper.