Cover slip or no cover slip

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sombre
Posts: 11
Joined: Mon Jul 30, 2018 8:14 am

Cover slip or no cover slip

#1 Post by sombre » Tue Jun 25, 2019 1:59 pm

Hi all,
I have recently just discovered the pleasures of creating crystal slides to photograph with I must admit mixed results.
My question is, should i place cover slips on my slides or will a cover slip prevent the crystals from forming?
If I should place cover slips on these slides, should I do so straight away while the slides are wet. Or wait till the slides have dried and the crystals have formed.
I would be extremely grateful for any advice.

Many Thanks
Last edited by sombre on Tue Jun 25, 2019 7:11 pm, edited 1 time in total.

MicroBob
Posts: 1298
Joined: Sun Dec 25, 2016 9:11 am

Re: Cover slip or no cover slip

#2 Post by MicroBob » Tue Jun 25, 2019 2:44 pm

Hi,
usually crystals will form with and without cover slip, but differently.
It is also possible to cover the crystals afterwards, but the mounting medium would have to be compatible with the substance.
Crystals often deteriorate over time which might be prevented or slowed down by mounting.

Bob

apochronaut
Posts: 2673
Joined: Fri May 15, 2015 12:15 am

Re: Cover slip or no cover slip

#3 Post by apochronaut » Tue Jun 25, 2019 3:22 pm

You will probably have to do some experimenting in order to determine the best approach for your purposes. No doubt the presence of a cover slip while the crystals are forming , will affect the speed and style of the formation.

but here are some general rules regarding the effect of immersion homogeneity or lack of, on the image quality.

1) All substances above the sample are part of the immersion medium: air,water,glass,air,water, glycerin or oil.
2) The higher the N.A. of the objective, the more a lack of immersion homogeneity affects image quality.
3) Air between the subject and the cover slip can severely affect image quality with higher N.A. objectives. If there is a large air space above the subject, it's deleterious affect can be partially counteracted by using very thin cover slips.
4)An objective's cover slip requirement is marked in one of three ways : - , means that it can or not be used with a cover slip: a numerical designation gives the optimal thickness of the cover slip under controlled optimal conditions : a 0 means it is to be used without a cover slip.
5) Generally, objectives below N.A. .40 are little affected by a lack of immersion homogeneity.
6) No cover objectives are preferable to cover corrected high N.A. objectives, if there is going to be a big lack of immersion homogeneity. A .90 no cover objective used without a cover, can easily achieve better results than a 1.30 cover glass corrected oil immersion objective if the ideal immersion conditions are too far off.

Hobbyst46
Posts: 2051
Joined: Mon Aug 21, 2017 9:02 pm

Re: Cover slip or no cover slip

#4 Post by Hobbyst46 » Tue Jun 25, 2019 3:49 pm

sombre wrote:Hi all,
I have recently just discovered the pleasures of creating crystal slides to photograph with I must admit mixed results.
My question is, should i place cover slips on my slides or will a cover slip prevent the crystals from forming?
If I should place cover slips on these slides, should I do so straight away while the slides are wet. Or wait till the slides have dried and the crystals have formed.
I would be extremely grate full for any advice.

Many Thanks
Crystallization occurs by various mechanisms. Two of them, for example, are evaporation and precipitation upon cooling, respectively.

1. Evaporation of the solvent (water, alcohol, or other) is most rapid when the slide is not covered. So the crystals dry over time, and the result is a layer of solid on the slide. To prolong the product's life, it should be kept in clean dry air. IMO, it is easier to keep all such slides in a closed (sealed if possible) container over drying powder, such as calcium chloride or silicagel. Homely alternative: A "Lock-Lock" flat rectangular box, containing a spoon of "Turbol" powder. Turbol is a drying powder for cabinets, pianos etc.
Of course it is also possible to make the slide initially in a form of a sealed chamber and crystallize the stuff within the chamber, and place a coverslip thereafter, but it is less convenient IMO.

2. Precipitation upon cooling works when the soluble stuff (say sugar) dissolves in hot water (or hot alcohol) more than it dissolves in cold solvent. So, you prepare a concentrated ("strong") solution in hot water, place a drop on a slide, place a coverslip and let cool. Next, it should be sealed to prevent evaporation of the solvent. I would make a 1-2mm deep chamber on the slide, in which the precipitation occurs, then seal around with nail polish.
Air bubbles might appear and interfere.

I assume that only objectives of low power and a WD of more than 1-2mm will be used.

Notes:
I have only done according to method 1, not 2.
Forum member RobBerdan has published a comprehensive guide for crystal preparation and microscopy.
Zeiss Standard GFL+Canon EOS-M10, Olympus VMZ stereo

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