Polarising

Do you have any microscopy questions, which you are afraid to ask? This is your place.
Post Reply
Message
Author
Glot
Posts: 65
Joined: Thu Oct 17, 2019 7:23 am

Polarising

#1 Post by Glot » Wed Feb 26, 2020 6:55 am

With regards petrographic thin sections. It is recommended to grind the glass slide flat which also textures the surface for adhesion. When I do that, under XPL, I don't get much extinction. That is, the frosted slide seems to re scatter the light. I get quite a lot of visible light comming through the frosted slide. I dont get that with a non frosted slide.
Comments/ advice?

MichaelG.
Posts: 2240
Joined: Mon Apr 10, 2017 8:24 am
Location: NorthWest England

Re: Polarising

#2 Post by MichaelG. » Wed Feb 26, 2020 7:54 am

The problem that you have found seems entirely logical
Sorry, but I struggle to understand the quoted advice.

... Could you give a reference, please ?

MichaelG.
Too many 'projects'

microb
Posts: 363
Joined: Wed Mar 27, 2019 6:39 am

Re: Polarising

#3 Post by microb » Thu Feb 27, 2020 7:16 am

When using adhesive on two CNCed acrylic lenses, they recommend not smoothing the interfacing surfaces because the adhesive sill optically smooth it all out. But that assumes a match in the index of refraction that smooths out the light path. AN artist putting together dichroic glass can hide the interface surfaces because of a closely match index of refraction between the adhesive and the glass.

This seems to suggest that the slide has a drastically different index of refraction from the optical adhesive being used.

MichaelG.
Posts: 2240
Joined: Mon Apr 10, 2017 8:24 am
Location: NorthWest England

Re: Polarising

#4 Post by MichaelG. » Thu Feb 27, 2020 8:27 am

For info.

Lakeside 70C adhesive/cement was recommended to me by a highly respected maker of thin sections ... http://www.lakeside-products.com/html/cement.html
Its properties are well-matched to glass microscope slides, with no need for surface roughening.

MichaelG.
Too many 'projects'

Glot
Posts: 65
Joined: Thu Oct 17, 2019 7:23 am

Re: Polarising

#5 Post by Glot » Mon Mar 02, 2020 9:53 pm

Loctite make two products thry recommend for this. Some commercial preparers are now using CA adhesive such as Loctite 460(?) however, my tests with cheap CA weren't that promising. Thermoplastic glue is very outdated but I guess if it works, why change. I have not located a supplier in Australia for small amounts of any specific adhesives.
The Loctite ones are AA349 ( uv cure, RI 1.4790) and EA E30CL ( 2 part, RI 1.5725). There are a number of resins specifically designed for this but hard to source and very expensive.

MichaelG.
Posts: 2240
Joined: Mon Apr 10, 2017 8:24 am
Location: NorthWest England

Re: Polarising

#6 Post by MichaelG. » Mon Mar 02, 2020 10:08 pm

Glot wrote:
Wed Feb 26, 2020 6:55 am
With regards petrographic thin sections. It is recommended to grind the glass slide flat which also textures the surface for adhesion.
Still hoping to see a reference to the source of that recommendation ...

MichaelG.
Too many 'projects'

microb
Posts: 363
Joined: Wed Mar 27, 2019 6:39 am

Re: Polarising

#7 Post by microb » Mon Mar 02, 2020 10:45 pm

Here's a link where this guys says to frost the slides:

https://youtu.be/zbG5E07EQy0?t=435

MichaelG.
Posts: 2240
Joined: Mon Apr 10, 2017 8:24 am
Location: NorthWest England

Re: Polarising

#8 Post by MichaelG. » Mon Mar 02, 2020 11:01 pm

microb wrote:
Mon Mar 02, 2020 10:45 pm
Here's a link where this guys says to frost the slides:

https://youtu.be/zbG5E07EQy0?t=435
Thanks for that ... I will watch it carefully tomorrow.

MichaelG.
Too many 'projects'

Glot
Posts: 65
Joined: Thu Oct 17, 2019 7:23 am

Re: Polarising

#9 Post by Glot » Tue Mar 03, 2020 7:57 am

They all say to frost the slides and flatten them. Amazing how un flat float glass is. The petrographic suppliers sell frosted and clear slides. The finished specimen needs to be between 29 and 31 microns so a flat slide is essential.
Attachments
thinsections.pdf
(33.83 KiB) Downloaded 179 times
Last edited by Glot on Wed Mar 04, 2020 12:32 am, edited 1 time in total.

MichaelG.
Posts: 2240
Joined: Mon Apr 10, 2017 8:24 am
Location: NorthWest England

Re: Polarising

#10 Post by MichaelG. » Tue Mar 03, 2020 9:21 am

Thanks for the pdf ... It confirms what I noticed in the video
They are ‘all’ using Epoxy to fix the sample to the slide
... I would respectfully suggest that is the reason why they find it necessary to roughen the surface of the slide:
III. Preparing the Glass Slide:
1. Glass slides have to be roughened or the epoxy will not stick and your thin section will fall off.


MichaelG.
Too many 'projects'

Glot
Posts: 65
Joined: Thu Oct 17, 2019 7:23 am

Re: Polarising

#11 Post by Glot » Wed Mar 04, 2020 12:35 am

A quick search will give you numerous instructional videos and documents from universities, colleges, equipment manufacturers etc.

MichaelG.
Posts: 2240
Joined: Mon Apr 10, 2017 8:24 am
Location: NorthWest England

Re: Polarising

#12 Post by MichaelG. » Wed Mar 04, 2020 7:40 am

Glot wrote:
Wed Mar 04, 2020 12:35 am
A quick search will give you numerous instructional videos and documents from universities, colleges, equipment manufacturers etc.
Sorry ... We’re obviously talking at cross-purposes:
I was trying to help with an an explanation/mitigation for the the problem that you were experiencing.
... I will be silent on the matter.

MichaelG.

...........
I get quite a lot of visible light comming through the frosted slide. I dont get that with a non frosted slide.
Comments/ advice?
Last edited by MichaelG. on Wed Mar 04, 2020 7:52 am, edited 1 time in total.
Too many 'projects'

Glot
Posts: 65
Joined: Thu Oct 17, 2019 7:23 am

Re: Polarising

#13 Post by Glot » Wed Mar 04, 2020 7:44 am

I appreciate any help or feedback.

jb89
Posts: 101
Joined: Fri Jun 21, 2019 9:09 am
Location: Denver, Co

Re: Polarising

#14 Post by jb89 » Wed Mar 04, 2020 6:02 pm

We use Hillquist adhesive at school and most of us do not bother to frost our thin sections, it will adhere fine either way.

If you can lay your slide on a flat and true surface and see any movement when you tap the corners you can either grab a different slide or you can grind them flat but frosting should not affect your ability to assess the specimen

Glot
Posts: 65
Joined: Thu Oct 17, 2019 7:23 am

Re: Polarising

#15 Post by Glot » Fri Mar 06, 2020 11:44 pm

I have come to the conclusion, with out testing my theory, so take it with a grain of salt. When I frost a slide, I am creating many fine facets. If the adhesive has a different RI, it will refract at those facets. This scatters the polarised light and de polarises it.
Bonding agents used in universities or commercial operations do not have the same cost restraints as me. For example, most sell in two litre containers for US$250 upwards plus almost as much freight. The thermoplastic adhesive mentioned above is well over $1000 Australian per kg. I have found a local product made by Norland. Also available through Edmunds in Australia.

Scarodactyl
Posts: 893
Joined: Sat Mar 03, 2018 9:09 pm

Re: Polarising

#16 Post by Scarodactyl » Sat Mar 07, 2020 12:19 am

Yes, an angled optical discontinuity will refract and mess up thr polarization of the light, so if you frost the slide your adhesive has to match the RI of the glass very closely or you'll have some trouble. Probably best to just not frost your slides if you don't have adhesive with the right RI.

MichaelG.
Posts: 2240
Joined: Mon Apr 10, 2017 8:24 am
Location: NorthWest England

Re: Polarising

#17 Post by MichaelG. » Sat Mar 07, 2020 7:59 am

Nicely summarised, Scarodactyl

MichaelG.
Too many 'projects'

jb89
Posts: 101
Joined: Fri Jun 21, 2019 9:09 am
Location: Denver, Co

Re: Polarising

#18 Post by jb89 » Sun Mar 08, 2020 7:28 am

I have a classmate who is currently doing research on low-cost adhesives that can be used as petrographic mountants.

If he comes up with anything useful I will let you know, I think he is testing around 40 types of adhesive

wstenberg
Posts: 232
Joined: Sun Jul 23, 2017 6:11 pm
Location: Dallas TX
Contact:

Re: Polarising

#19 Post by wstenberg » Sun Mar 08, 2020 5:10 pm

At work we use plastic slides for thin sections, and we first grind them flat and polish to 800 grit. Then use use a refractive index matched adhesive that seems to fill in the polishing marks. It's all part of a system called Technovit by EXAKT.

Here's a link to a video showing the adhesive and how we glue up our slides.

https://www.youtube.com/watch?v=ShnPhEN9pH0
William
Dallas, Texas

Zeiss Standard WL with POL
Zeiss Axiomat
Zeiss Universal
Zeiss Stereomikroskop

Glot
Posts: 65
Joined: Thu Oct 17, 2019 7:23 am

Re: Polarising

#20 Post by Glot » Wed Apr 01, 2020 9:01 am

Jb89. Be very interested to hear conclusions. I have identified a couple of UV cure. Viscosity is a bit high at 2000 but found one that is 300 and RI of about 1.53. UV cure. Haven't tried it yet. I like the idea of controlling the rest time before cure to allow the bonding agent to flow very thin. The same reason for a low viscosity. I have measured s
Idea up to 20 micron variance over their surface but so long as I grind the billet accurately, that isn't an issue but I like the idea of grinding the slide flat first.

Post Reply