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Subject:	Re: OT: reminiscences
From:	R Sedlak <[log in to unmask]>
Reply To:	TechNet E-Mail Forum <[log in to unmask]>, R Sedlak <[log in to unmask]>
Date:	Sat, 1 Sep 2007 07:06:07 -0700
Content-Type:	text/plain
Parts/Attachments:	text/plain (56 lines)

Fish Glue/Bichromate photoresist was still being used a few years ago to make television screens... in quite large volume.
Rudy Sedlak
RD Chemical

Brian Ellis <[log in to unmask]> wrote:
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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