Crossed polarisation of salt crystals

The following salt crystal is seen using x20 objective on LOMO Polam P-113 Polarising Microscope.

The crossed polarisation images required a lot longer exposure on my Bresser Mikrocam 5.0 MP microscope camera and this has shown up a lot of hot pixels.

So, for the first time ever, I took a dark frame and subtracted it from each image using PIPP software (Planetary Imaging Pre-Processor, https://sites.google.com/site/astropipp/)

You can see the effect below – it is quite dramatic!

The following is from

https://www.hamptonresearch.com/documents/product/hr007641_cg101_salt_or_protein_crystals.pdf :

“A protein crystal, unless it is cubic, will typically be weakly birefringent under cross polarizers. Salt crystals are typically strongly birefringent under cross polarizers. Some plastic plates and materials are also birefringent so this test is more easily performed and interpreted in an all-glass environment or in a plate made from a low birefringent plastic.”

The initial photos show birefringence but I would not describe them as highly birefringent…..that is until you get to the 11x objective photos at the bottom of the post – now that is a highly birefringent salt crystal!


Crossed-polarisation image x3.5 objective (dark frame subtracted in PIPP, cropped and changed to greyscale in GIMP2). The salt crystal shows birefringence:

Bright field image, x20 objective:

Crossed-polarisation images before dark frame subtraction in PIPP, x20 objective:

Same fields of view as above but this time after dark-field subtraction using PIPP, x20 objective:

x11 objective, post subtraction dark frame with PIPP – for some reason the salt crystal on top right is particularly highly birefringent (below):

Bright field vs. Crossed Polarisation filters of slide cultured in pot pond at LRO 27/5/2018

LOMO Polam P-113 microscope.

Microscopy forum posts discuss using polarisation to view microscopic slides of pond life – apparently it can be quite spectacular! Well, my observations today were not spectacular but I had some success – see below…


x11 objective, bright field – a piece of pond weed (below):

This is the most successful observation today. The above field of view after introducing crossed polar filters (below, showing bi-refringence in the plant material) (x11 objective):

The following is a little weird – bi-refringence at the edge of the cover slip! (Below, again x11 objective):

However other parts of the slide do not show bi-refringence, such as this collection of material (below, x11) – bright field followed by crossed polars (there is a tiny amount of bi-refringence only at the lower right):

I had hoped to get more luck at higher magnifications – here is a slide at x20 – crossed polars followed by bright field (below):

LOMO Polam Fossiliferous Steinheim Impact Crater Lake Bed Miocene crossed-polarisation using LOMO Polam microscope

LOMO Polam Fossiliferous Steinheim Impact Crater Lake Bed Miocene crossed-polarisation using LOMO Polam P-113 microscope.


x11 objective:

x20 objective (panorama of 15 frames) – two fossils present with birefringence in crystals in the matrix in which they are embedded: