Thanks, Rich Abbott.
abbott@ligo.caltech.edu

We always used to use a lens tissue moistened with a bit of xylene to clean the oil off oil immersion lenses, and this is the procedure recommended in an article, "Immersion oil and the microscope", by J. R. Cargille, President of Cargille Laboratories, the outfit that makes most immersion oils. In his article he points out that synthetic oils such as those manufactured by the Cargille Co. have a number of advantages over Cedar oil and other natural oils (i.e. they contain no volatiles, do not degrade from exposure to light and normal temperatures, etc.) If you'd like a copy of this article, send me your FAX number and I'll send it off to you. In any event, I think you should be particularly careful not to use acetone or alcohol, because they will soften and dissolve the cement that is usually used to hold the lenses in place. Best of all, check with the manufacturer of the lens.
Wil Bigelow
Wil_Bigelow@mse.engin.umich.edu

Greetings,
Will Bigelow wrote:

[snip]... In any event, I think you should be particularly careful not to use acetone or alcohol, because they will soften and dissolve the cement that is usually used to hold the lenses in place. Best of all, check with the manufacturer of the lens.

What is the reason for xylene being less likely to dissolve cement than acetone or ethanol? I would have thought that it depended on the cement and that generalizations would be difficult. Thanks for any insight on this.
Tobias Baskin
baskin@biosci.mbp.missouri.edu

We've used xylol for the last 30 years here with no serious consequences on any of our Zeiss and Leitz objectives. The service people use a combination of ether and other stuff, but we don't need it often enough to deal with having a can of ether on hand. Xylol should work fine, but never use alcohol or acetone on objectives. Mike
Michael L. Boucher Sr.
Boucher@TCRCA.USBM.GOV

The original question referred to a situation where it was indeed necessary to clean cedarwood oil off an immersion lens. However, in routine use of an oil immersion lens, it has been my understanding over the years that it is best not to clean the lens. We use commercial non-drying immersion oil, and merely wipe the excess oil off the lens with a tissue after use.

A. Kent Christensen, University of Michigan,

I agree that xylene and alcohol are probably equal. An old Leitz Ortholux manual warned against using "spirits" to clean lenses. Modern cements are unlikely to be affected by either, but I still choose to use them sparingly. I always use 6" cotton-tipped applicator sticks and, after dipping them in xylene, press the bud against a tissue until it is just damp. It makes more sense than soaking the lens and cleans just as well. I also follow up with a dry bud when cleaning oil from a 40X objective. Then, I use the same method with Windex or other commercial glass cleaner to remove all traces and clean the lens thoroughly.

Cotton tipped applicators have an enormous advantage over lens paper. They work better on small, concave, or recessed lenses, they aren't touched by your fingers, and so never transfer skin oils, and they prevent contact between your skin and any toxic solvents (such as xylene) you may use.

I never use acetone on an objective. Some (mostly American Optical) have a painted "mask" around the lens, and acetone can dissolve the mask and deposit the paint onto the lens.

Rick Markgraf
rlmarkgraf@ucdavis.edu

According to the article by Cargille that I referred to earlier, Prof Christensen is correct. High grade synthetic immersion oils should be resistent to oxidation and should contain no volatile materials, and therefore should not form gummy deposits, and should not need to be cleaned from lenses with a solvent.

Natural oils, such as Red Cedar oil, may contain volatile components, and are likely to be subject to oxidative degradation, and therefore often leave gummy residues if not thoroughly removed from the lens.

W. C. Bigelow
(bigelow@umich.edu)

     Wow, did I open a can of worms when I mentioned the article on immersion
oils by J. J.Cargille.  Actually, the article was written in 1964, and is
possibly quite a bit out of date by now.   Basically it covers the following
points:
      1.   describes the function of immersion oil in increasing the
numerical aperture of a lens by increasing the refractive index between the
objective and condenser.
     2.  Discusses the problems involved in formulating immersion oils,  most
of which are of no direct concern to users of them.
    4.   Notes that a variation of 1 C in temperature can change the
refractive index of an oil by approx. 0.0004, so be sure to work at the temp
given on the bottle
    5. Synthetic oils can be formulated to have better properties than most
natural oils;
          - freedom from color which may degrade performance 
          - lower volatility and more resistant to oxidation and
photo-decomposition, and so less likely to thicken and to form a gummy
deposit on the lens.   Wont thicken over time and change ref. index.
         -  lower acidity and so less likely to damage your instrument, 
    He also mentions that although Red Cedar oil has been one of the most
commonly used oils: it has poor adsorption characteristics because it may be
discolored; it contains volatiles and will leave gummy films on lenses unless
cleaned off promptly, and it may thicken over time due to evaporation and
change refractive index; it usually has a relatively high acidity, and so may
be prone to damage the objective with prolonged use.
   He does not explain why it is common practice to use xylene to clean
immersion oil off lenses, except to say that it doesn't damage the lens
cement.  I don't know whether this is the solvent recommended by all
manufacturers of microscopes.  In these times when such a wide variety of
cements are available there may be some exceptions.  However, I did check the
instructions for a Nikon microscope we purchased only a couple of years ago,
and xylene was recommended there.
     The rule I facetiously give to my students concerning the approach to
using instruments is,  "After all the controls are bent and everything is
completely fouled up, read the instruction manual!"
     The present address of the Cargille Company is:  R. P Cargille
Laboratories,  55 Commerce Road, Cedar Grove, NJ, 07009   (Ph. 201-239-6633; 
Fx:  201-239-6096)  if you want more up-to-date info on immersion oils.
     Sorry to get everyone so stirred up:
           Wil Bigelow

       (bigelow@umich.edu)




Going back a few years, as I do unfortunately, I remember the Microscope
Service Engineer telling me never to use Xylene as it dissolved the mounting
medium of the lens. He always used Ether.


The problem was he used to chuck the Ether soaked lens paper into the metal
wastebin. He also used to smoke. And smoking wasn't banned in the Lab in
those days. (I said I went back a few years). When he also threw his
cigarette end in the bin, the result was exciting, (excessively so) to say
the least. 


I still use Xylene. Nothing fell out yet. :)


Regards

Stephen Griffiths

e-mail s.griffiths@ucl.ac.uk



It seems that there are quite a lot of different methods of cleaning
lenses. My favourite method, for what it is worth, is to use either a
proprietary mixture form Leica here in Sweden (isopropanol, some detergent
and dist. water, I think)  or abs. ethanol (both are OK from the
manufacturer). After wiping the excess oil off around the lens (never on
the lens), I put a drop of this on the lens, let it sit for a while, then
blow it off in one go with clean compressed CO2. I repeat as many times as
necessary. In this way I never need to touch the lens surface which
according to many authorities (e.g. Shinya Inoué in his book "Video
Microscopy") may be detrimental as the surface coating of the lens is very
soft and easily scratched or abrased even by "soft" cotton or lens cleaning
paper.

    I prefer not to use solvents like xylene due to their potential health
risks which I think should be considered in this context.

    Finally, it would be nice if reps. from each of the large microscope
manufacturers could give the final words in this matter (what is best for
the lenses, what can the cement take, what if there is other stuff than oil
to clean (e.g. Moviol or other mountants), what is the best way to clean
non-oil immersion lenses that have been messed up with oil or other
things).

Stefan Gunnarsson

e-mail Stefan.Gunnarsson@devbiol.uu.se



I use Kodak lens cleaner on a cotton swab and blot with a clean cotton
swab (Q-tip will do) for both oil immersion and non-oil immersion lenses. 
It's certainly of less of a health threat than xylene or chloroform and
since it comes in a squeeze bottle is not likely to become contaminated by
dipping cotton swabs into it.
 

De Irving

dirving@aggie.pw.usda.gov



We have been using Q-tip brand cotton swabs dipped in chloroform to clean our
Zeiss objectives.  The method works extremely well, and requires a minimum of
scrubbing.  Using this method over the past 7 years has resulted in no
problems.  I would caution that other cotton swabs may
scratch the lenses.

  Doug Keene

DRK@shcc.org



I was recommended to clean any gunked up lens with a knob of polystyrene
foam - no chemicals, just the dry foam rubbed in a circular motion onto the
lens. Over the years none of my Zeiss lenses has suffered any damage from
this.



Diana van Driel

dianavd@eye.usyd.edu.au



I was advised by my microscope rep. (a very respected microscopist) to use a
heavy polishing compound (like used to remove paint on cars) and light grit
sandpaper to remove oil and lens coatings on our lenses.  On particularly
difficult occasions a sandblaster has sufficed.  Needless to say that in 23
years we have experienced no difficulty using this method.  We have never
published a paper based on our findings but we hope to get a Science article
soon.


I thought that with the huge influx of postings regarding this issue I would
just add my 2 cents worth as it seems everybody had a different idea about
how to do it.  You should contact you local microscope rep. if you need to
know how to clean a lens.

goulette@bme.jhu.edu, nikon@jagunet.com




We use Kodak lens cleaner for routine cleaning, plastic dropper bottles
are refilled from the more affordable quart containers. Chloroform is
reserved for obstinate deposits, like when someone immerses a non-DPX
lens into the DPX or Permount. 


A couple of microscope technicians that have worked on our equipment use 
lighter fluid.  It dries without leaving a film and yet is claimed not to 
attack lens adhesives or coatings.  Has anyone else used lighter fluid on 
lenses?  Personally, I've only used to take scuff marks of vinyl 
flooring.


Regards,



Glen MacDonald

glenmac@u.washington.edu




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