The excellent result that Eric achieved for his replica Omnia serial number plate.
Subscriber Frank Foster, 25 Abbey St., Fairhaven, Massachusetts, sent in copies of two 'Letters to the Editor' of Stationary Engine magazine. He thought they would be of some interest to his fellow subscribers. We therefore reprint them with gracious permission form Stationary Engine.
The first letter, which appeared in the August 1994 issue of Stationary Engine, was written by Bryan Robert, Rad-book Green, Shrewsbury, and reads as follows:
'Dear Editor: In David Edging ton's article in the April (1994) issue he mentions the frustration of the restorer who is missing the spec plate. I have had some success etching a brass plate in the way the electronics enthusiast makes his printed circuit board.
The first step is to lay out some etch resistant lettering on a brass plate; transfer lettering (Letraset) with its various styles and sizes is ideal. For borders and larger areas, shapes cut in plastic electrical tape rubbed down hard on the surface, can be used. Curves, etc. are filled in by hand, using model paint (curves are available on Letraset Ed.)
'The completed mask is then placed with the etch ant in a plastic tray (margarine tub) which, if floated in a bowl of hot water (to speed reaction), will etch sufficiently if agitated for 10 to 15 minutes. If left too long, the lettering may be undermined.
'After etching, the masking is removed (cellulose thinners work well for this) and the whole plate is given a light 'blow over' with matte black aerosol. The tops of the lettering can then be polished with some fine emery paper on a flat block.
'The et chant used is ferric cholo ride, which is available from Tandy Stores or your friendly chemist. For those not familiar with this stuff, be wareit's poisonous, corrosive and will turn your bathroom suite, clothes, fingers etc. a nasty yellow!
'I recommend doing some experiments before an elaborate mask is made, but my results were quite successful.'
Mr. Robert's letter was followed two months later, in the October 1994 issue of Stationary Engine, by a letter from Eric Brain, Clutton, Bristol, in which Mr. Brain related the following story about plate etching:
'Dear Editor: The letter from Bryan Robert in the August 1994 issue could not have come at a more opportune time.
'I have a Hewlett & Blondeau Omnia engine (subject of an article in Stationary Engine issue No. 198), which is missing a serial number plate.
'With a view to making a replica plate I had already found a photograph of one, which was kindly supplied by Philip Galli more some years ago. I scaled it up, using my existing screw hole centres on the water hopper as a standard.
'The very next day my Stationary Engine magazine arrivedlo and behold, Bryan Robert was advising on the very method with which I intended to try an experimental nameplate.
'By the end of the week I obtained some ferric chloride crystals from an electronics shop ( kilo for 1.75) and made a trial plate which, on completion, so exceeded my wildest hopes that further attempts were not necessary. The plate was left in the solution of hot liquid et chant for 1 hour 10 minutes, which gave a perfect depth with minimal undermining of the masking.'