Polarizers discriminate between diatoms and mineral detritus

Here you can discuss different microscopic techniques and illumination methods, such as Brightfield, Darkfield, Phase Contrast, DIC, Oblique illumination, etc.
Post Reply
Message
Author
Hobbyst46
Posts: 4277
Joined: Mon Aug 21, 2017 9:02 pm

Polarizers discriminate between diatoms and mineral detritus

#1 Post by Hobbyst46 » Sat Aug 04, 2018 8:44 pm

Hello,

A strew slide of lab-cleaned environmental diatoms shows, besides diatoms, particles of mineral detritus, such as quartz and mica. These are birefringent, whereas diatoms are not (AFAIK). A demonstration of the difference is quite trivial, but IMO is fun, so I posted it.
Done with anyman's POL microscopy: the fixed analyzer linear polarizing sheet (cheap polaroid) is stuck below the trino head, the rotatable polarizer placed over the field diaphragm.
Diatoms were cleaned by boiling in water, then heating in 3% H2O2, then treatment with home stain remover (details will be given in another post). This is a wet mount, in water.

All photos are single images, brighfield (+POL). Colors are slightly modified in Rotation4 since the original was too bluish to my taste.
Dark spots that are neither diatoms nor quartz/mica are possibly organic detritus.
Attachments
Start.JPG
Start.JPG (288.86 KiB) Viewed 2601 times
Rotation1.JPG
Rotation1.JPG (303.98 KiB) Viewed 2601 times
Rotation2.JPG
Rotation2.JPG (300.87 KiB) Viewed 2601 times
Rotation3.JPG
Rotation3.JPG (310.91 KiB) Viewed 2601 times
Rotation4.JPG
Rotation4.JPG (288.59 KiB) Viewed 2601 times

User avatar
75RR
Posts: 8207
Joined: Sun Oct 12, 2014 2:34 am
Location: Estepona, Spain

Re: Polarizers discriminate between diatoms and mineral detritus

#2 Post by 75RR » Mon Aug 06, 2018 6:08 am

Re: Polarizers discriminate between diatoms and mineral detritus
Indeed it can!
With a low magnification lens it can be a quick and easy way to separate diatoms and birefringent detritus - also makes for a very attractive view as well,
but there are times when birefringence is the equivalent of light pollution when it is right next to or worse yet below the subject one is photographing when using DIC!
Zeiss Standard WL (somewhat fashion challenged) & Wild M8
Olympus E-P2 (Micro Four Thirds Camera)

Post Reply