NavList:

Gary asked

"So back to my original question, can I use some florescent paint to restore the bubble illumination?"

The answer is that he can, but not by over-painting with modern photoluminescent paint. I have tried it and it doesn't work, presumably because there is insufficient energy escaping and alpha particles have a very short range, so they don't penetrate very far into the paint overlay.

The solution is to scrape off the old paint and dispose of it. If you don't eat it or breathe in the dust, you should come to no harm. You could bury it in your back garden or, if excessively conscientious, consult the physics department of your local university. Having removed the old paint, you replace it with modern photoluminescent paint. It is often sold as "luminous paint", but it has to be charged by exposing it to light for a few minutes. It then emits light for between forty minutes and several hours, depending on the grade of paint.

I describe the process to be followed here: http://sextantbook.com/2008/12/ for an AN5851 bubble sextant, and it is very similar for the A7. Rotate the eyepiece to 45 degrees and remove the four cheese headed screws thus exposed. Remove the two cheese headed screws below the bubble control. Invert the bubble chamber to expose a large black washer held in place by three small countersunk screws. Remove these and carefully prise up the washer with a sharp blade to expose the paint. The rest is as on the web site: a layer of white paint on the undersaide of the washer where there was previously radium paint. When dry, add a thick layer of photoluminescent paint. Paint some on to the glass as well, but omit the white paint here. Charge the paint by shining a bright light e.g 40 watt bulb into the eyepiece for 5 minutes.

Bill Morris
Pukenui
New Zealand

----------------------------------------------------------------
NavList message boards and member settings: www.fer3.com/NavList
Members may optionally receive posts by email.
To cancel email delivery, send a message to NoMail[at]fer3.com
----------------------------------------------------------------