How to remove fungus from old Diatom slides

[deBult]

May I ask your combined knowledge for assistance please.

I bumped into a box of 85 old Diatom slides. Age unknown but the glass of the slides looks and 'feels' very old (typical streaks like you see in windows panes begin 1910).
Descriptions in Chinese ink or in pencil. All slides show different Diatom samples - most from the UK and some from New Zealand. Very well cleaned diatoms, mounted with xxx? and the thickness of the mounting layer is a bit on the high side. Coverslips appear to have a variance in thickness as well.

Nearly all slides are full of fingerprints and have a slight cover of fungus on them. I cleaned the first 5 using soap en water, minding not to touch the stickers with descriptions. Fungus ad fingerprint were easy to remove.

Question 1: what is you guidance in cleaning the rest of the slides. In particular how to prevent h fungus from coming back (the description stickers were not cleaned to prevent damage .. so still contain some of the fungus fibers).

Question 2: Some slides have a lacquer? ring around the coverslip: the rings show severe damage. How to salvage them (or alternatively leave as is?)

Best, Maarten

[JB]

Hi Maarten,

Fungus grows only if there is enough moisture (more than 60 %). Without moisture, it will not grow back. Store it in a dry room or in an airtight box with some fresh silica gel.

UV light also kills fungus and fungus spores. You can expose the slides to some UV (sunlight or a 365 nm lamp) but really, the important thing for the future is dry storage.

There used to be an instruction for restoring the rings here https://www.mikroskopie-forum.de/index.php?topic=17423.0 but the images are lost.

Best wishes,

Jon

[anne]

Hallo Maarten,
die schwarzen Ringe bestehen oft aus einem alkohollöslichen Lack (Ruß in Schellack). Daher ist es den Versuch wert es mit Alkohol zu lösen. Aber Achtung evtl. ist auch das Einbettharz löslich in Alkohol. Ringlack erhält man bei Michel Haak um neue Ringe zu ziehen.
Das überstehende Harz im ersten Bild kann man vorsichtig mit der Rasierklinge oder Skalpel abkratzen und dann das Präparat auch mit einem Ring versehen.
lg
Anne

[deBult]

Thank you Jon and Anne.

Will work on the Lack and let you know.

Best, Maarten

[deBult]

Well started cleaning the slides WITHOUT the lacquer ring first and discovered more about the age: one slide is dated 1862.

Most of the sticker labels and the handwriting are in the same style, no clue yet on the name of the maker.

Best, Maarten

[deBult]

The cleaning of the slides without the ringed coverglasses works out OK.

Tried removing the cracked lacquer rings without success: tried IPA, ETHANOL, several different density petrol derivates. Did not risk soaking the in fear the mounting would be damaged.

I do not have Xylol: would this be an option?

Guidance appreciated,
Best Maarten

[JB]

Hi Maarten,

I think you shouldn't try to remove the existing rings. If they are in such good condition, just leave them as 19th cen. (?) originals.

Usually people look for methods to clean the immersion oil without damaging the rings. I think the best would be petroleum ether (Wundbenzin) which cleans the oil quickly without damaging the ring. Ethanol is known to damage the rings (shellac dissolves in ethanol).

Best wishes,

Jon

[Bob]

Hi Maarten,
to find out more about the ring lacquer you might try to dissolve some flakes, away from the slide.
This is for sure a nice find!

Bob

[deBult]

Hi Maarten,

I think you shouldn't try to remove the existing rings. If they are in such good condition, just leave them as 19th cen. (?) originals.

Usually people look for methods to clean the immersion oil without damaging the rings. I think the best would be petroleum ether (Wundbenzin) which cleans the oil quickly without damaging the ring. Ethanol is known to damage the rings (shellac dissolves in ethanol).

Best wishes,

Jon

John,

Thanks for feedback, most of the ringed slides have a severely cracked lacquer ring.

Have not yet tried immersion for imaging: as stated in the opening post: there is substantial variance in thickness of the coverglasses and mounting-medium (and also in the object-slides have a huge variance in thickness: some are so thick you cannot Kohler the condenser diaphragm). So was limiting-myself to max 40* na 0.7 for now.

Some of the object-slides look like pre 1900 window pane glass (streaks, small bubbles etc.).

The diatoms themselves are very well cleaned though.

[Hugo Halfmann]

Hallo Maarten,

für die Lackringe wurde neben Schellack (alkohollöslich) auch Asphaltlack verwendet (xylollöslich). Die Krakeleerisse sprechen m.E. für Schellack. Der löst sich allerdings nur langsam in Alkohol.