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.
- 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
- Rasied 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!