Attempts at Diatom Arranging

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KurtM
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Attempts at Diatom Arranging

#1 Post by KurtM » Fri Aug 07, 2020 12:30 am

Greetings, all: One of the things I have been dabbling around with off and on for the past few years is becoming proficient at micromanipulating diatoms, for the purpose of making strews that are free of detritus, creating type slides, and possibly arranged slides. A few days ago I was practicing moving diatoms around when it just sort of turned into an arrangement, and I have been following this direction since with two definite goals in mind: a) learn how to accurately place and position the valves, and b) learn how to finish a permanent mount without wrecking the design. I'm not investing too much time or effort into the first part until I master the second, so these arrangements aren't the prettiest you ever saw. I will be considering them crash test dummies until I get a better handle on the mounting part.

Diatoms are best mounted in a high refractive index mountants, which require "curing" by heating until solvents are driven off. This process causes the mountant resin to bubble, and for strew slides this doesn't matter but it's not hard to imagine what the boiling does to arrangements. So part of this nutty endeavor is to figure out how the masters of the art did it.

The pictures are in proper order, and start with that practice session that just sort of turned into an arrangement. The second pic shows what happened when I tried to cure the Naphrax mountant. The second arrangement was lost in a stupid accident I don't wanna talk about. The third might wait a bit while I do some Naphrax curing tests to figure a few things out. The last picture shows the tip of a Bic ballpoint pen next to the third arrangement for scale. It's always fun to see that the ball is nearly twice the diameter as the arranged diatom pattern!
Attachments
8-3-20 first attempt arranging.jpg
8-3-20 first attempt arranging.jpg (62.11 KiB) Viewed 1198 times
8-5-20 first attempt after cure.jpg
8-5-20 first attempt after cure.jpg (74.16 KiB) Viewed 1198 times
8-5-20 second attempt arranging.jpg
8-5-20 second attempt arranging.jpg (134.36 KiB) Viewed 1198 times
8-6-20 third attempt at arranging.jpg
8-6-20 third attempt at arranging.jpg (85.77 KiB) Viewed 1198 times
8-6-20 a wider view.jpg
8-6-20 a wider view.jpg (118.55 KiB) Viewed 1198 times
Cheers,
Kurt Maurer
League City, Texas
email: ngc704(at)aol(dot)com
https://www.flickr.com/photos/67904872@ ... 912223623/

BramHuntingNematodes
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Re: Attempts at Diatom Arranging

#2 Post by BramHuntingNematodes » Fri Aug 07, 2020 1:41 am

Very nicely arranged. Do you use some kind of albumen to adhere them to the slide?

I have many large American sweetgum trees; someday I'll get around to tapping one. The ancients use chloroform, but I might try some different solvents.
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75RR
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Re: Attempts at Diatom Arranging

#3 Post by 75RR » Fri Aug 07, 2020 5:46 am

This is probably why (subconsciously) I have avoided diatom arranging/mounting. I imagine it can on occasion be somewhat frustrating!

A newbie question: Does a slower evaporation help? As in, do they cure themselves in time?

The ballpoint pen photo is really quite dramatic - good composition.
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Re: Attempts at Diatom Arranging

#4 Post by Hobbyst46 » Fri Aug 07, 2020 6:41 am

Wow, Kurt, you are doing well !

As it happens, since June I am struggling with the same challenge, but the only ambition is to free the diatoms from fine silt.
I am using Pleurax, not Naphrax.

For adhesive I am trying 2% gelatine in 1:1 water/isopropanol. Without acetic acid, since glacial AA is not a safe home chemical (IMO).
After I arrange them (in a straight line) I humidify the gelatine layer by means of an inverted beaker, lined from the inside with moistened filter paper.

Yesterday was the first time ever that diatoms stayed on the permanent slide and were not swept away.
I find that the centrics are easier to play with than the pennates.
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Re: Attempts at Diatom Arranging

#5 Post by MicroBob » Fri Aug 07, 2020 7:54 am

Hi Kurt,
this looks like a very promising start!
I think for diatom arranging three steps are necessary:
- dropping and orienting the frustule
- solidly fixing it to the cover slip
- embedding it in the mountant

For me a thin shellac layer and a thin layer of skin fat worked well for mounting in Aroclor acetone mix. The fixing is done by heating to 90degree, the acetone doesn't dissolve the shellac.

Bob

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Re: Attempts at Diatom Arranging

#6 Post by Hobbyst46 » Fri Aug 07, 2020 8:29 am

Again, thanks, Kurt, for posting ! most encouraging !

MicroBob wrote:
Fri Aug 07, 2020 7:54 am
...- solidly fixing it to the cover slip- embedding it in the mountant.
For me a thin shellac layer and a thin layer of skin fat worked well for mounting in Aroclor acetone mix. The fixing is done by heating to 90degree, the acetone doesn't dissolve the shellac.
Indeed, solidly fixing is a challenge (for me at least).
Pleurax is dissolved in IPA. Logically, the appropriate adhesive for solid fixing should not dissolve in IPA.
I tried fixing with a thin layer of Pleurax (as a separate step before mounting). But it did not hold them and they were swept away by the mountant.

Water-soluble adhesives should be candidates, provided that they do not dissolve in IPA. Not an easy restriction to meet.
Gelatine dissolves in cold water (I made 2-3%), adding IPA did not cause turbidity or flocculation.
I tried a very thin layer of gelatine on the coverslip. It fixed the diatoms, humidified after placement. Fixing was not solid. They spread around.

Just now tried a thick layer of gelatine; the layer was visible by color reflection zones (like Newton rings). Again, the diatoms were inhibited from sweeping away by the mountant, but the initial pattern (a straight row) disappeared and they were randomly dispersed all over the coverslip on the slide.
Shellac is soluble in alcohol and melts (certainly when heated to 180C as is the protocol with Pleurax), so maybe inappropriate for Pleurax. I did not try it yet though.
Admittedly I did not try the intermediate step of heating to 90C. I am doing all this with an alcohol burner.
So, will try gelatine AND heating, as suggested by Bob.

BTW, Rod's (rnabholz) trick, of resting the slide a few mm above the hot surface by means of small metal clips, is extremely useful. It prevents spillage of heated Pleurax onto the metal surface and shifts of the coverslip, that ruin the diatom arrangement.
See response no 358 in this thread:
viewtopic.php?f=10&t=3036&start=330
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Re: Attempts at Diatom Arranging

#7 Post by MicroBob » Fri Aug 07, 2020 11:03 am

When I tried soap embedding chrome alaun gelatin was suggested as a very resistant glue layer. Another method was the use of animal glue, especially sturgeon bladder glue that is still made in small quantities, I think for gold plating. There also were sugar based glue recipes. Recently in this forum polyacrylamide was suggested, which I would like to try when I find the time.
With Pleurax the fairly high temperature might be a problem as many substances don't stand it. Perhaps the cover slip can get just a bit of Pleurax and the main volume of Pleurax can be heated on the slide instead.

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Re: Attempts at Diatom Arranging

#8 Post by Charles » Fri Aug 07, 2020 1:14 pm

Hi Kurt,

Moving frustules while heating the mountant has been a constant problem in my mounts. Can you explain your method? What adhesive did you use? After arranging and before the mountant, did you dry the adhesive first by heating? Did you use a drop of solvent (Toluene)first to evacuate the air in the frustules? How many drops of mountant did you use, just one on the arrangement? In my diatom permanent mounts, the larger and not so flat diatoms seem to move the most. I'm about done with sorting my three diatomite samples and will be ready to do some permanent mounts soon. We can compare notes.

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Re: Attempts at Diatom Arranging

#9 Post by Element 56 » Fri Aug 07, 2020 6:03 pm

Nice work Kurt. Other than a quick non-permanent spread I only attempted to mount a single diatom once. Unfortunately I used the wrong medium and it's almost impossible to find on the slide!

Kirby

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Re: Attempts at Diatom Arranging

#10 Post by KurtM » Fri Aug 07, 2020 6:41 pm

Doron & Bob: Although definitely a Pleurax fan, I'm not attempting to use it for this purpose. I have export version Naphrax from Brunel UK and Toluene for this work.

However ... forum member keithstout and I have been discussing possibilities of modifying the Pleurax curing progression, and he is conducting experiments with lower temperatures with longer cook times as a result. I have had success getting Pleurax to fully cure using ~130C @ 8 hours, for instance. But that's still only good for strews due to bubbling. I think it's possible to use lower temperatures and longer cook times, and in fact, think that may be where it has to go with any diatom mountant.

Charles: The procedure I've been using lately looks to be pretty much what you do, as far as I can tell. I'm working with a similar micro-manipulator, a stereo microscope, using the adhesive recipe you provided, moving the slides by hand, etc. In answer to your questions, no no heating to dry out the adhesive, and no, no toluene application.

My idea is to place a small drop of Naphrax on a slide, then place the coverslip with arrangement onto that; and then place the slide on the digital hot plate for curing. With Naphrax I'd start at 90C, step up to 100C after half an hour or so, then leave it there at 100C for a good while, say 4 to 6 hours. This has worked okay for some strews.

But the trouble is, the single small drop of Naphrax I apply to the slide doesn't spread out when I lay the coverslip on it. I have to mash down on the coverslip to make it spread, which is fine for strews but death to arrangements. Pre-heating a drop of Naphrax on a slide doesn't help, get the same thing. I guess next up is experiment with further thinning the Naphrax, which is already of a watery consistency.
Cheers,
Kurt Maurer
League City, Texas
email: ngc704(at)aol(dot)com
https://www.flickr.com/photos/67904872@ ... 912223623/

Hobbyst46
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Re: Attempts at Diatom Arranging

#11 Post by Hobbyst46 » Fri Aug 07, 2020 7:38 pm

KurtM wrote:
Fri Aug 07, 2020 6:41 pm
Doron & Bob:...However ... forum member keithstout and I have been discussing possibilities of modifying the Pleurax curing progression, and he is conducting experiments with lower temperatures with longer cook times as a result. I have had success getting Pleurax to fully cure using ~130C @ 8 hours, for instance. But that's still only good for strews due to bubbling. I think it's possible to use lower temperatures and longer cook times, and in fact, think that may be where it has to go with any diatom mountant.
...
But the trouble is, the single small drop of Naphrax I apply to the slide doesn't spread out when I lay the coverslip on it. I have to mash down on the coverslip to make it spread, which is fine for strews but death to arrangements. Pre-heating a drop of Naphrax on a slide doesn't help, get the same thing. I guess next up is experiment with further thinning the Naphrax, which is already of a watery consistency.
Pleurax is a just a polymer dissolved in IPA. IPA is volatile, and should be removed by the mounting process. Theoretically, from the volatility aspect, I estimate that switching the curing temperature from 180C to 130C will lengthen the curing time by a factor of ~2^5, that is ~30: say, from 15 min (at 180C) to 7.5 hours. So, 8 hours at 130C sounds very reasonable. Although, when using an alcohol burner, 15min at 180C is much more practical IMHO.

However, one other function of the heating is to lower the viscosity of the resin so it permeates the frustule. The effect of heating on this function is difficult to estimate in the absence of very specific data, and it depends on the structure of the frustule as well (hole diameter, etc). Unfortunately, the less viscous and more fluid the mountant, the higher chance that diatoms detach...

The same principles are valid for other resins, IMO.

Edit: if heating the gelatine adhesive will not attach the diatoms, will switch to the Gum Tragacanth recipe.
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Re: Attempts at Diatom Arranging

#12 Post by Charles » Fri Aug 07, 2020 10:31 pm

KurtM wrote:
Fri Aug 07, 2020 6:41 pm
I guess next up is experiment with further thinning the Naphrax, which is already of a watery consistency.
Kurt, I think you should go thicker. The more Toluene you use to dilute the more it will bubble? Also try heating the adhesive after the arrangement.

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