microscope graticule cleaning - recommendations required

I've finally got around to cleaning up the optics on my OMT microscope. The eyepiece heads, or 'oculars' contain a 3" glass disc which you can see in the picture below. What you cant see in the picture are the myriad of microscopic graticules, thread profile lines and cross-hairs that lie on the surface of the glass.

Also sitting on the glass unfortunately is 70 years of doom and gloom which I would like to try to remove. Having previously successfully dissolved numbers on an old watch face with alcohol I'd like avoid making a similar mistake this time.

So, are there any experts in the house that can enlighten me and comment on:-

a) how were the graticule lines actually created on glass in the 1940s~50s era ?

b) what would be a safe cleaning solution and method to remove the contaminant ?

Gerry

Make sure you have glass and not plastic and soak in a bath of ordinary washing up detergent such as Fairy Liquid. Keep just luke warm to start with and leave for an hour or so to soften up the stains before gently rubbing with a soft cloth or sponge. Rinse with luke warm water.

The graticule lines could have been engraved or produced photographically and etched with hydroflouric acid.

Edited By old mart on 31/12/2020 19:27:35

Gerry,

I would expect your graticule lines to be have been aluminised, by deposition ... but other materials and techniques are available.

Probably best to start here: **LINK**

https://www.graticulesoptics.com/manufacturing

and see if you recognise any similarities.

Edit: Do you have another microscope available, to take some photos ?

As for cleaning ... I would avoid anything approaching abrasion !

My favourite ‘wash’ for dirty optical components is [believe it or not] a dilute solution of Alberto Balsam ‘Tea Tree Tingle’ shampoo in distilled water ... I don’t know why it works so well, but it does !

MichaelG.

Edited By Michael Gilligan on 31/12/2020 19:31:33

Hi there, Gerry,

A retired professional microscopist * I used to meet at club meetings advised me that he used 'spit' (i.e. saliva) for cleaning small areas. Just make sure you haven't recently been eating liquorice! Oh, and toothpaste is abrasive too!

He applied his 'spit' on a cotton bud BUT BEWARE!!! Standard cotton buds can contain sharp silica particles. You can, however, find grit-free cotton buds if you search diligently. A friend with optical interests advised me that ordinary paper tissues can also contain sharp particles - he advised me that kitchen roll is free of nasties (I presume that is because kitchen roll is made from recycled paper fibres). Then there are special lens-cleaning tissues available from some opticians, laboratory suppliers or eBay. One well known make to look for is 'Whatman', the same people who make the filter papers.

Best regards,

Swarf, Mostly!

* He wasn't originally a professional microscopist but an amateur. When it was realised that asbestos was a health risk, his manager appointed him as 'the asbestos man' and the search for asbestos fibres took over the rest of his career!!

Thanks chaps for all your comments. And I have some very good news !

As you suggested Michael I did have another microscope with which to look at the 'printing' more closely. What I quickly discovered was that the marking wasn't on either side. Its on the inside !!! The disc is comprised of two glass discs bonded together. One can clearly see this at the periphery and the bore where there are a few trapped bubbles close to the chamfered edges of each disc. .....I wondered why I wasn't able to carefully feel the 'printing' with a pin !

So cleaning worries are no more ,but i will still be careful to avoid scratching.

As for the actual coating, I'm not so sure its an aluminised type Michael. I have a 1970s marching compass and that has what I guess is an aluminised line on one of its windows. When I put that under the microscope its very obviously a metallic material when you get the lighting in the right way. The lines on the OMT disc don't have any of this kind of appearance. They just look like 'black paint' from every possible angle. I'll try to get some pics later and dig into the possible processes that may have been used and let you know if I reach any conclusions.

Gerry

Good news indeed, Gerry

In my defence: I did write:

“ I would expect your graticule lines to be have been aluminised, by deposition ... but other materials and techniques are available. ... ”

... So I was only a little bit wrong

MichaelG.

Edited By Michael Gilligan on 04/01/2021 17:03:30

If the glass is laminated, avoid soaking it and use cool water, not luke warm. Any separation of the balsam will start at the outside edges and you will have to live with any that is present. Don't be tempted to clean the edges of the plate.

Edited By old mart on 04/01/2021 17:46:46

Cleaning of optical lenses and graticules, after many years at Leica the standard cleaning agent is Ether.

Do not flood any lens or glass, a slightly ether moistened 'Q' tip and gently clean dirt and oil, grease away, maybe two or three times.

If you have a clean Selvyt cloth then gently polish one way. If no selvyt cloth then washed clean cotton, ie. handerkerchief..

There are some photo/camera cloths available which do a good job as well.

Oh dear, all you microscopists aren't going to like this so turn away now if you have feelings for lenses.

In the words of Bernard Cribbins "we wos getting nowhere" ! I began to clean the lenses and graticule discs as carefully as possible, fluids and no abrasion etc, but in the end only mechanical removal worked. The culprits were these things.....

100% of the glass surfaces seemed to be covered in these myriads of fine lines which where interspersed with white dots. Invisible to the naked eye, these dots were very tenacious, quite hard and almost crystaline in their texture. I found the only way to shift them was to take a new flat-edged scalpel blade and run it carefully over the surfaces.

I couldn't detect that the scraping with the steel blade left any mark on the glass, but if it did it was invisible to my small 20/40x microscope.

I'm puzzled as to what might have created this phenomena. I have heard of fungus being a problem on lenses, but fungus doesn't normally follow straight lines, does it ?. So perhaps it was the deposits of some kind of spider or mite?

I have more lenses to do. What are your thoughts on the use of an ultrasonic cleaner next time ?

Gerry

Fungus growth usually creates more of a fog effect with permanent etching. I have had lenses with a pattern similar to yours that were described to me by older experienced technicians as a glass eating bacteria, usually from instruments stored in a damp high humidity area. Extreme cases looked like a vine pattern nearly covering the area.

Those pesky cosmic rays causing trouble again!

When I was trained a a scietific instrument maker,the lens cloths we used were old cotton hankerchiefs which had been washed many times, and breathing on the lens,of course we were fitting new lenses some with graticules,which I believe were made by a photographic process,I was once given the job of renovating an instrument with a graticule made by the very old method of using a spiders web secured by(if i remember correctly) sealing wax.the only one that I ever saw,replacement was a modern graticule.