Diatoms mounted in titanium dioxide (Horace Dall slide)

[JMC]

I recently had a Horace Dall diatom slide arrive on which the diatoms had been mounted with Titanium dioxide. The slide was made in 1950 and this procedure was done to increase their refractive index.

I have done some quick test images of the slide (two objectives - Olympus Splan 20x NA0.46, and a Zeiss 63x NA0.9 on my Olympus BHB). Darkground and brightfield images using a white LED light. The colours from the diatoms are as captured by the camera, they have not been added by me. I presume the Titanium dioxide forms layers on the diatoms which then interacts with the light, a bit like the surface of an interference filter or on an oil film. The slide itself does have a sort of sheen to it when you get the right angle with the light.

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20x darkground.

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Another region, 20x darkground.

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63x brightfield.

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63x darkground.

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[MichaelG.]

Way out of my depth here, JMC

All the microscopy-related references to titanium dioxide seem to be about nanoparticles
… except, of course, those touting slides by Horace Dall

Do you have any references to his mounting technique, that you could share please ?

Thanks
MichaelG.
.

Just found this, but it doesn’t get me much further:
https://slideplayer.com/slide/12991909/

[Phill Brown]

Are you using the 0.9 dry? they can be silvered also using the same chemical process as mirrors.
Silver nitrate. Super shiny and reflective.
Excellent image capture.
Things must be fairly well lined up.
Coated coverslip.
Coated sapphire watch glass I have only found from 1mm x18mm onwards.

[JMC]

Way out of my depth here, JMC

All the microscopy-related references to titanium dioxide seem to be about nanoparticles
… except, of course, those touting slides by Horace Dall

Do you have any references to his mounting technique, that you could share please ?

Thanks
MichaelG.
.

Just found this, but it doesn’t get me much further:
https://slideplayer.com/slide/12991909/

There's not a lot on it Michael, at least not a lot that I have found yet. There is an article in the Quekett Journal, 1985, vol 35, p280-285 "Mounting methods for high resolution optical microscopy", H.E. Dall, which does describe some of it. It looks like the TiO2 ones were relatively early attempts and were quite dangerous to do, as they relied on fuming titanium tetrachloride. The resultant TiO2 layer is about 50nm thick. The experiments were done "...when suitable winds would quickly evacuate the fumes.".

[JMC]

Are you using the 0.9 dry? they can be silvered also using the same chemical process as mirrors.
Silver nitrate. Super shiny and reflective.
Excellent image capture.
Things must be fairly well lined up.
Coated coverslip.
Coated sapphire watch glass I have only found from 1mm x18mm onwards.

Yes, it's a Zeiss Neofluar pol objective and is 63x, NA 0.9, which I use dry. I've tried to align everything as best I can.
Not sure about the transmission properties of the Dall slide and coverslip. Plan is to measure the transmission spectra tomorrow. That'll give me an indication of whether it is worth imaging in the UV (I suspect 365nm will be ok, but not 313nm). If I image in the UV I'll lose the lovely colours (monochromatic imaging) but might squeeze more resolution out.

[photomicro]

I would have expected better contrast from such a slide.

I have a few of this type, albeit from more modern mounters than Horace Dall. The coating metal is often different too, aluminium being quite common.

This is of one by John Dale.

Mike

[Phill Brown]

It is remotely possible the coverslip is a UV/IR filter to increase the visible spectrum sensitivity for film.
Making it impressive as it should be to the human eye or for printed reproduction which is out of fashion.
Seeing coated drill bits it's not hard to imagine the choice of coating as shiny yellow,which doesn't exist other than an illusion on RGB.
The world we perceive is a reflection of what happened very recently rather than a projection (mostly).
I keep banging on about RGB but colour prints are not to be sold short.
I last used a 50" Dolby 1080 plasma for checking my images when it mattered as reference,glad I kept it rather than sold it for peanuts.
Things have moved on and progress seems only relative to the backdrop of current events.
Sometimes it's just about being there to see it for yourself anyway.
I rest my case but still always happy to be corrected.

[JMC]

I would have expected better contrast from such a slide.

I have a few of this type, albeit from more modern mounters than Horace Dall. The coating metal is often different too, aluminium being quite common.

This is of one by John Dale.

Mike

From what I read in the Quekett Journal article mentioned above, the TiO2 one I have seems to be an early attempt. He went on to do aluminium coating using a vacuum setup, and that this process gave 'visibility of the finest detail.'. I've not seen any of the aluminium coated ones so can't comment on how they compare to mine, but from his description it looks like they were an improvement over the earlier ones.

EDIT - I found a paper which talks a bit more about aluminium coating of diatoms - https://www.researchgate.net/publicatio ... _Frustules

Not a mention of Horace Dall's pioneering work in it though, nor in some of the other papers I've been reading.

[MichaelG.]

There's not a lot on it Michael, at least not a lot that I have found yet. There is an article in the Quekett Journal, 1985, vol 35, p280-285 "Mounting methods for high resolution optical microscopy", H.E. Dall, which does describe some of it. ...

Many thanks for the reference.

MichaelG.

[Greg Howald]

Well done! Diatoms are great. Made from glass, they don't fall apart so easily as other microbes.

[Phill Brown]

I just have diatom slide envy which I never even knew was a thing until recently.
I'll get through it rather than over it.

[MichaelG.]

Many thanks for the reference.

.

Having found the article, I note the brevity of his description of the process.
… Perhaps this was his subtle way of discouraging the dabbler !

For what it’s worth [and in the hope that the Quekett will raise no objection], I have copied those few words, to inform further discussion:
.

D52C5374-97CF-4BD6-B592-344452A82B61.jpeg (200.75 KiB) Viewed 3746 times

.

My first thought being that “mounted in” is a somewhat surprising way of saying “coated with”

MichaelG.

.
P.S. __ I have just seen your own interesting page on the subject:
https://jmcscientificconsulting.com/mic ... d-diatoms/

[Phill Brown]

I guessed it was safe to assume they where not mounted in the stuff.
The fumes are now known to reduce the resolve to supply accurate information.
Thanks for sharing the canada balsam info,it smells so good,why bother with anything else, apart from styrax,which I can't decide whether it smells exotic or not nice at all,depends on the mood most likely.
Deception by omission is still deception though,commercial gain has been a strong motivation for a while on and off.
Still like the coated coverslip effect though,and all fancy slides should be ringed in black.

[Scarodactyl]

I wonder if a sputter coating would work.

[dtsh]

I wonder if a sputter coating would work.

That was my assumption, not sure how else you'd do it without laying down too much and obliterating detail.

[MichaelG.]

I guessed it was safe to assume they where not mounted in the stuff.

… and yet, Dall uses the description “in the form of an embracing coat”

At the risk of playing with semantics … If the coating is on the underside of the coverslip AND ‘embraces’ the diatoms, then it is contiguous, and might thereby merit the use of “mounted in”

MichaelG.

.
Edit: __ This, from 2018, is very interesting:
https://www.cambridge.org/core/services ... py-div.pdf

[Scarodactyl]

I wonder if a sputter coating would work.

That was my assumption, not sure how else you'd do it without laying down too much and obliterating detail.

This sounded more like chemical vapor deposition, though I am not an expert on the practicalities of these methods. Physical vapor deposition should have the advantage of not requiring any titanium tetrachloride anyway. I think some people do it at home if I remember right. I assume it wasn't so easy to do back in the 50s, hence the more dangerous route. Or maybe the coating is too thin?

[Phill Brown]

I guessed it was safe to assume they where not mounted in the stuff.

… and yet, Dall uses the description “in the form of an embracing coat”

At the risk of playing with semantics … If the coating is on the underside of the coverslip AND ‘embraces’ the diatoms, then it is contiguous, and might thereby merit the use of “mounted in”

MichaelG.

.
Edit: __ This, from 2018, is very interesting:
https://www.cambridge.org/core/services ... py-div.pdf

Hats off for the excellent theory.
There is a colour change at the margin that suggests the coverslip is likely coated on the outside at least.
Easier to coat both sides with PVD.
Standing on the shoulders of giants combined with a leap of faith that the description would not be deciphered by the perspective buyer.
Packaging can be intended to mislead,the average double decker often doesn't contain exactly what it says on the tin.

While the coating process is being run for a commercial product it would be easy enough to include your mates project into the chamber for the duration

[JMC]

Well this post has moved on since yesterday. Thanks for all the comments, makes for interesting reading.

The coating on the outside of the slide is interesting, I hadn't thought of that and assumed it was just on the inside face. I've got a reflection probe for my spectrometer, so next time I am using it I'll test the slide and coverslip. Not sure if it'll tell me much, but might give an indication of gross differences and if it is 'glass' vs 'coated glass'.

In a break from work, I also had a look at the slide using visible light brightfield imaging using a Leitz PL APO 100x 0.60-1.32 oil immersion objective (wide open at NA 1.32). Condenser was a Olympus Aplanat and I was using it with the condenser pulled to one side to try and give some oblique lighting. Light source was a white LED, and imaging was done on a unmodified Canon EOS 5DSR. Attached below are a few of the psychedelic images (colours are as captured). Images have been reduced in resolution for sharing here. Single images - no stacking.

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And a crop from the above image kept at the original pixel resolution.

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Also, an image of the objective (now one of my favourites).

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[Phill Brown]

Thanks for sharing,Some credit where it is due. That's a pretty good resolution from here,it's early days with the slide too. I get nervous getting that close but sprung with a stop properly adjusted helps,It's a fair safety net and will have saved a few slides by now.
I broke a slide one time,not a big historic loss but I don't like breaking things,My oil objectives prefer to be stored in a cool dark place.
I haven't been motivated to try them in a long time,the minimal FOV can feel like standing in front of a wall and staring hard at the finish.
It's just a personal thing though as that resolution has it's place in understanding the structurer.
Top result I say.

[JMC]

In a desperate attempt to stave off work for a few minutes, I thought I would share some images from some slides I recently received from the Postal Microscopical Society. These are Aluminium coated ones by John Dale (who has been mentioned above). These were imaged on my modified Olympus BHB with a 60x NA1.4 Splan APO and using a warm white LED light. Imaged using a monochrome converted Nikon d800.

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[zzffnn]

Amazing contrast and dotting power. Almost like SEM. Oblique light stacking, I am guessing? Offset oblique or circular oblique light, with or without polarization? Thank you, JMC.

[JMC]

Amazing contrast and dotting power. Almost like SEM. Oblique light stacking, I am guessing? Offset oblique or circular oblique light, with or without polarization? Thank you, JMC.

Thanks. No polarisation. Just bright field, but my Olympus Aplanat can be pulled to one side which was done here (I guess that is 'offset oblique'). Although to be honest, straight bright field gives pretty much as good an image. Yes, I love the look of these slides - a bit like SEM as you say.

These are all individual photos - no stacking.

Jonathan

[Hobbyst46]

Beautiful images, JMC !!

The properties of titanium oxide are definitely tempting to use as high RI medium, however it will only work in a film form or a suspension of nano particles, both of which are not really realistic under home microscopy...

[JMC]

Beautiful images, JMC !!

The properties of titanium oxide are definitely tempting to use as high RI medium, however it will only work in a film form or a suspension of nano particles, both of which are not really realistic under home microscopy...

Thanks. Yes, these metal oxide or metal layers certainly make for nice images. As you say though, they're not really something that cam be easily done at home as standard preparation techniques. If I ever get myself a sputter coater I'll see if I can make some of my own, but for now I have no work projects which would require one.