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!