Large diatoms in air, on a nail polish layer

[Hobbyst46]

I received beautifully cleaned large Pinnularias and Surirellas from Northern Germany (thanks, MicroBob), that look under the stereoscope (60X) like 3D natural gems. Ordinary mounting in resin under a coverslip crashed them, in spite of the fairly thick layer of resin. So I tried mounting in air, in a chamber (well) slide. A coverslip top for the well is compatible with the 25x0.45 Plan achromat objective, and protects the diatoms from ambient dust.

My previous attempts to attach a coverslip supported on thin glass fragment or aluminum foil supports have failed. So I followed MicroBob's suggestion and supported the coverslip on a stainless steel shim-ring. Dimensions of the ring are: OD=18mm, ID=12mm and 0.1mm thickness.

I prepared two glues, by fully dissolving gel nail polish in acetone by intensive shaking or stirring in hermetically-sealed tubes/vials. Concentrated glue is a solution of 2-3 drops of nail polish in 2ml of acetone. Dilute glue is a 1:10 dilution of the concentrated glue in acetone. These ratios are crude guide lines, since gel nail polish is not a standard stuff.

A little concentrated glue is sucked into a 1ml plastic syringe, equipped with a blunt #27 needle. 2-3 tiny drops of glue are placed, by slow injection, at equidistant locations on the shim ring. A clean slide is immediately placed, face down, onto the ring for temporary attachment. Gentle finger pressure is applied. Curing under UV (1-2 hours with a black light tube; a few minutes with a nail-polish UV lamp) makes the attachment permanent.

Next, diatoms were mounted. A drop of dilute glue was placed on a clean round 18mm OD coverslip. It spread and the acetone rapidly evaporated to leave a nearly transparent stain. Diatoms were transferred from the storage slide to the coverslip. One brightfield image, taken with the 40x0.75 objective, shows a 205um long Pinnularia half-sunk into the nail polish glue. Nevertheless, the glue layer was thin enough, for most of the diatoms to stay attached to the glue layer, without sinking.

To cover the well, 3-4 drops of concentrated glue were placed on the shim ring (on the slide), the slide was inverted onto the coverslip, such that the ring exactly overlapped the coverslip, and was left to cure under UV. The final thickness of the layer on top of the slide, including the ring, coverslip and glue layers, is 0.2mm, measured with calipers.

Imaging was mostly done with the 25x0.45 Plan objective. Darkfield was achieved with either the ordinary LED lamp of the microscope and D position of the turret condenser, using water instead of oil, to contact the slide bottom; or with my home-developed slide edge on-stage illuminator. Edge illumination slightly improves the 3D view of the image, IMO. Note the girdle view of the Pinnularia.

The Cymatopleura, in contrast to the other diatoms, is quite flat, so its image is flat...

Some images were slightly post-processed as mentioned in the titles, and all were resized.

ID's of the diatoms are tentative.

I plan to ring the slide as usual, with direct-on-dust paint.

[Hobbyst46]

(continued)

[MicroBob]

Hi Doron,
nice preparations and images! These really are big and beautiful diatoms. The Cymatopleura have a wavy surface, very beautiful when seen at an angle or from the side. I just got a small sample of the new Speedax and will try it on this material.

Bob

[Hobbyst46]

Thanks, Bob.