Brian,
There is certainly technical content in what you wrote, but to keep
certain people happy, I have added the NTC.

Most of us aren't even 59, let alone have any neat stories like that.
Ever thought of writing an autobiography?
Bev
RIM



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
Sent: Saturday, September 01, 2007 3:31 AM
To: [log in to unmask]
Subject: [TN] OT: reminiscences

When I was a student, in 1948, I took a summer job with a company making

aircraft gyroscopic gunsights. My work involved:
1. mixing potassium bichromate with fish glue
2. applying a coat of this mix to a very thin blackened steel sheet
3. after drying, exposing same to UV light through glass photographic 
plates with registration pins, turning over and doing the same on 
t'other side (different plate)
4. developing the image with hot water
5. etching the sheet in nitric acid
6. rinsing in clean water
7. stripping the resist in boiling strong sodium hydroxide solution

The result was about twenty graticules with two curved, very fine, 
slots. If two were placed back-to-back, depending on their respective 
positions, two dots of light shone through. These were projected on a 
half-silvered mirror and the gunner would turn a knob to align the two 
dots of light with the wingtips of the enemy aircraft, to get the range.

This was a very hazardous job but it was my first (but not last!) 
experience of using a photoresist for etching a metal. Can anyone beat 
this kind of work, going back 59 years? :-)

Brian

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