Thermography

Very high class social sta­tion­ery was tra­di­tion­ally engraved — this is an expens­ive pro­cess because a fresh plate must be engraved for every design.  The incisions formed by the engraver are filled with ink and this is trans­ferred to paper under great pres­sure.  Print­ers longed for a way to cre­ate the same effect using their exist­ing lead types and print­ing presses.

Ther­mo­graphy stepped in to meet this need.  The pro­cess in out­line is –

• Print an art­icle (say, an invit­a­tion) in the usu­al way
• Dust the still-wet ink with a spe­cial ther­mo­plastic powder (‘Ther­mo­graph­ic Powder’)
• Remove any sur­plus powder so that the powder only remains on the pre­vi­ously prin­ted area
• Apply heat to the invit­a­tion — the powder reacts by fus­ing to the ink and lift­ing from the surface

The end res­ult is a sel­dom-seen effect of type that stands proud of the sur­face of the card or paper.

The powder was avail­able before machines could apply heat; and print­ers were encour­aged to exper­i­ment with whatever they had avail­able: an elec­tric fire or grill could be pressed in to ser­vice to apply heat!  Adana launched their first basic machine in 1950 which took already-dus­ted art­icles on a con­vey­or belt through a tun­nel that held heat­ing ele­ments.  Later iter­a­tions of machines from Adana and Caslon took a freshly-prin­ted doc­u­ment; applied the ther­mo­grap­ic powder; shook off the excess; passed it through the heat­ing tun­nel and dropped the doc­u­ment on the oth­er side of the machine.  Caslon took the machines fur­ther and developed products to sit at the end of auto­mat­ic, high-speed presses.

Powders are avail­able in three main vari­et­ies: clear (takes on the col­our of the under­ly­ing ink); gold (to be used with a yel­low base) and sil­ver (to be used with a blue or grey base).  Dif­fer­ent grade powders are also avail­able depend­ing on the thick­ness of the strokes to be covered: thin strokes need a finer power, but this raises from the sur­face less than a coars­er powder.

Practical Hints

• Ther­mo­graphy relies on good print­ing early on — poor print­ing can­not be improved by this pro­cess — so you’ll need excel­lent start­ing material
• If the res­ult is a dull, mottled sur­face then too little heat is being applied
• Flat, blotchy res­ults come from too much heat being applied
• Ther­mo­graph­ic powder will stick to any­thing, so greasy fin­ger marks on card will attract the powder and so have a raised sur­face at the end of thermography
• One approach to applic­a­tion is to stack the prin­ted objects; pour powder over the sur­face to be ther­mo­graphed; draw the top sheet up and shake off the excess.  The second sheet will now be exposed from the pile and have the sur­plus power roughly where needed.  Repeat this process
• Raised print­ing will mean your fin­ished batch of sheets will be deep­er at one side than anoth­er.  This will dis­tort cut­ting and you should use paper at the fin­ished size when you begin thermography
• Paper jams might res­ult in paper touch­ing the heat­ing ele­ment of the machine: be ready to deal with a small fire!