Thoughts about diatom cleaning

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Hobbyst46
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Thoughts about diatom cleaning

#1 Post by Hobbyst46 » Sat Apr 28, 2018 9:40 am

Hello all,

Various methods of cleaning diatoms from ambient sources (collected from coasts, rivers, lakes) or cultivated as cultures have been published. Having some fun with cleaning epiphytic diatoms with bleach, bleach+acid, hydrogen peroxide+acid, I noticed that many frustules were destroyed. My most recent disappointment is a sample of Mediterranean diatoms, collected from beach algae, where many of the elliptical and especially triangular and rectangular
frustules (please excuse my taxonomy ignorance) disintegrated or even completely disappeared upon cleaning. That cleaning was 3h boiling in H2O2, rinse, heating in HCl, rinse, keep in 50% ethanol. All intermediate rinsing and liquid exchanges were done by 10min centrifugations at 500 rpm. No further intense shaking or mixing. Why such damage to the frustules?
"Naturally" one suspects the physical impacts of centrifuge, boiling, handling etc. Plus some comments in the literature about the relative fragility of certain marine diatoms, etc.
My wish was to obtain "just" nice, clean, whole frustules, coming out of a mixture of debris...
However, as a beginner, I found out that the silica skeleton is an intricate structure that consists of organic and siliceous components (see, for example, links below). The organic components contribute to the mechanical stability of the frustule. So, even when the starting material is pure, alive diatoms in clean water, the percentage of transparent clean frustules may well depend on the chemistry used for cleaning, rather than the physical forces exerted on them.
There is a method of mildly cleaning diatoms with a detergent (SDS) + calcium complexant (EDTA). It apparently leaves the frustules intact, but does not remove most of the organic matter. It has been applied to diatoms in culture, i.e. a relatively clean sample. Maybe it could serve as basis for a method that will sufficiently remove organic matter to yield a whole but clear frustule.
Just a thought. At least regarding the suspicious contribution of rough handlings of collected diatom during cleaning.

Article:
http://bora.uib.no/handle/1956/15756
Review:
https://www.researchgate.net/publicatio ... ng_Forward
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Re: Thoughts about diatom cleaning

#2 Post by zzffnn » Sat Apr 28, 2018 12:30 pm

500rpm is too fast. Please try gravity precipitation, hand centrifuge or something around 30rpm.

Some diatom species, such as some triangular one I had before, will disappear even after gentle boiling. There is not much that can be done with those.

Steve Beats (a highly experienced UK diatomist) once told me that many fresh (non-fossil) diatoms can be cleaned well by gentle boiling in water (and collected by gravity+sieving through filters). Controlling continuous bubbling rate and duration is key though. Too much will destroy some diatoms, while too little may not do anything. I have not had chance to try it myself though.

I don't know how much of protection can EDTA offer, when detergent (SDS) is there.

You probably already know, bleach+acid releases toxic chlorine gas, so you cannot do it a large scale.

If you are very carful and have professional experience with chemistry and lab safety, then you can try soaking in concentrated sulfuric acid (don't heat it, unless you have a lab fume hood). I won't recommend it to regular folks without professional lab experience though, as it may easily burn you.

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Re: Thoughts about diatom cleaning

#3 Post by Hobbyst46 » Sat Apr 28, 2018 2:01 pm

Thanks zzffnn!
zzffnn wrote:500rpm is too fast. Please try gravity precipitation, hand centrifuge or something around 30rpm.
I intend to do so with my future fresh sample, which I need to collect within the present alga blooming season. I am under the impression that the use and details of centrifugation varies among labs (and home labs). I had a temporary access to a friend's centrifuge. I don't have one at home.
Romman et al, in the article linked to above, centrifuged highly complex and sensitive diatoms (as they describe it) - Coscinodiscus centralis Ehrenberg and C. wailesii Gran - at 4500g and the frustules did not fall apart, as shown by their SEM images. They claim, that if a treatment is good for these diatoms it will succeed with others.
Some diatom species, such as some triangular one I had before, will disappear even after gentle boiling. There is not much that can be done with those.
Personally, I like those triangles very much. They deserve a second chance...
...many fresh (non-fossil) diatoms can be cleaned well by gentle boiling in water (and collected by gravity+sieving through filters). Controlling continuous bubbling rate and duration is key though. Too much will destroy some diatoms, while too little may not do anything. I have not had chance to try it myself though.
Maybe instead of boiling one can heat in a water bath at 80C, say, at the price of a x4 longer process time. Worth trying.
I don't know how much of protection can EDTA offer, when detergent (SDS) is there.
I think that EDTA, combined with SDS, serves to enhance the extraction of proteins, mucus and polysaccharides from the live diatom. Whether it works by pulling out calcium from structures, or in other ways, I am not clear.
You probably already know, bleach+acid releases toxic chlorine gas, so you cannot do it a large scale.
Yes, absolutely. I applied them in sequence, not simultaneously. Bleach, rinse, HCl.
...concentrated sulfuric acid...
No, I prefer milder chemicals, not oxidizing or hygroscopic acids. If I find a miniature high-temp oven, maybe try incineration instead.
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Re: Thoughts about diatom cleaning

#4 Post by zzffnn » Sat Apr 28, 2018 4:16 pm

I was told that cleaning is mainly done by the stirring and bursting action of bubbles (no bubbles, no cleaning). So just heating itself may not work. You may run side by side experiment and report back :mrgreen:

Gravity precipitation of frustules finishes quite quickly, actually, in matter of say 5 minutes. So Better be on the safe side, I think. Many diatomists believe high speed centrifugation breaks frustules, but I have not tested such claims. I would get a hand centrifuge cheaply from eBay, if I were to get one. When I worked in a research lab and span down live cells, I used no more than 400rpm (cannot remember the g number).

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Re: Thoughts about diatom cleaning

#5 Post by MicroBob » Sat Apr 28, 2018 7:49 pm

Hi Doron,
this is a topic I am interested in very much. I haven't heard of SDS for use in diatom cleaning before, but I think it is very likely that it can do part of the cleaning. EDTA is a complex builder that brings elements into solution that are not suluble on their own like lime or iron.
What I have tried with some success is pancreatin, ground pankreas from pigs. It is sold as medicine in gelantine capsules, but there is something else in the capsules that I had to filtrate out. I have documented this method here: http://www.mikrohamburg.de/Programm/Pro ... 170917.pdf
This will be a very soft tratment for the diatoms.

There are two types of EDTA, they are better soluble in water with somewhat higher pH value.

These ovens were in use for enamel hobby work in the 1970s and can be bought here in Germany used for ca. 50-100€.

I thought about an even simpler method: A stainless steel disc of 30mm diameter and 4-5mm thickness with a hole from the side to fit a temperature feeler in it. The temperature feeler would be grip and thermometer at the same time:
https://www.ebay.de/itm/LCD-Display-Typ ... 2129ba1d95
My temperature feeler didn't last long though used at 900°C.
Glass quickly becomes softer at over 500 °C so the temperature has to be limited.
Heating a cover slip with fresh diatoms with an alcohol or gas burner to 500 °C leads to oxidation of the organic material. Salt could be removed afterwards with water, lime with EDTA or vinegar concentrate. The diatoms stick to the cover slip and colonies stay attatched. It is a quick way to get slides that are nice to look at but not as sterile clean as the H2O2 and acid process.

Your diatoms may have busted because something in their structure has expanded in the media you have used. The structure of diatoms is very different depending on species and location. I can very well imagine that there are diatoms that behave like this when beeing cleaned.

There are electric kitchen ovens that clean themselves by heating to about 450 °C. These are probably also usable for diatom cleaning.

Since the old processes with concentrated acids are not suitable for most hobbyists it is very worthwhile to look for alternatives. If they result in an acceptable permantent slide with not too much effort most hobbyists will be perfectly happy with the result.

Let's see what methods we can find.

Bob

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Re: Thoughts about diatom cleaning

#6 Post by Charles » Sat Apr 28, 2018 8:05 pm

I have not known of any acids destroying or degrading diatoms but bases will. So don't let the diatom sample soak in bases like chlorox for more than 4 hrs. I think most of your destruction is being caused by the centrifuge.

I use H2O2 18-30% boil for 30-60 min, and then add K2Cr2O7 (Potassium Dichromate) a few grains at time until the reaction stops. I let it settle for 8-12 hrs, siphon off 2/3 of the solution and then add HCl 30% and heat to boiling for 30-60 minutes (I do this outside as well as the H2O4S). Let settle for 8-12 hrs and siphon off the HCl and then finally add H2O4S 98%. I just let it sit in it for 24 hrs and siphon it off and start rinsing with distilled water for at least 6 times, letting the sample settle 8-12 hrs between rinses. After the rinses and if there are fine grit in the sample, filter through 25-20 Micron filter and reverse rinse the sample in the filter into a beaker. If the diatoms are still 'dirty', I add some pure soap flakes, stir it up and let set for not more than 1 hr and run it through the 20 micron filter and rinse thoroughly with distilled water until all the soap is gone. Then reverse rinse the sample back into a beaker for a final DW rinse.

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Re: Thoughts about diatom cleaning

#7 Post by desertrat » Sat Apr 28, 2018 8:16 pm

@Charles, now that's some serious, old school diatom cleaning! I like it! 8-)
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Re: Thoughts about diatom cleaning

#8 Post by MicroBob » Sat Apr 28, 2018 8:45 pm

Hi Charles,
thank you for describing you process in this detail.
What keeps me from organizing the needed substances is that I do all my microscopy work in a normal household with two teenage boys and a wife. I do many other things here and have no permanent laboratory set up. In my view a kitchen table in a turbulent household is not the best place for safely using strong acids. So for me it is very valuable to find ways that offer quick results which can be handled under my circumstances.

Bob

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Re: Thoughts about diatom cleaning

#9 Post by Hobbyst46 » Sat Apr 28, 2018 9:48 pm

Charles wrote:I have not known of any acids destroying or degrading diatoms but bases will. So don't let the diatom sample soak in bases like chlorox for more than 4 hrs. I think most of your destruction is being caused by the centrifuge.

I use H2O2 18-30% boil for 30-60 min, and then add K2Cr2O7 (Potassium Dichromate) a few grains at time until the reaction stops. I let it settle for 8-12 hrs, siphon off 2/3 of the solution and then add HCl 30% and heat to boiling for 30-60 minutes (I do this outside as well as the H2O4S). Let settle for 8-12 hrs and siphon off the HCl and then finally add H2O4S 98%. I just let it sit in it for 24 hrs and siphon it off and start rinsing with distilled water for at least 6 times, letting the sample settle 8-12 hrs between rinses. After the rinses and if there are fine grit in the sample, filter through 25-20 Micron filter and reverse rinse the sample in the filter into a beaker. If the diatoms are still 'dirty', I add some pure soap flakes, stir it up and let set for not more than 1 hr and run it through the 20 micron filter and rinse thoroughly with distilled water until all the soap is gone. Then reverse rinse the sample back into a beaker for a final DW rinse.
Thanks, Charles. I was much impressed by the methodology and fine results in your post of 2016/7 about doing diatoms. Here, I am just thinking of doing without these relatively harsh treatments. Cannot bring home H2SO4, for example. About acids in general: Intuitively, I would indeed expect that diatoms dissolve in basic pH and not in acid pH, but literature articles claim that some weakly silicified frustules do dissolve in acids as well (though slower than in base). The articles in the links above explain it, IMO. And, IMHO, according to the literature, the issue of potential damage due to centrifugation varies from lab to lab.
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Re: Thoughts about diatom cleaning

#10 Post by Hobbyst46 » Sat Apr 28, 2018 10:05 pm

MicroBob wrote:...
What I have tried with some success is pancreatin, ground pankreas from pigs. It is sold as medicine in gelantine capsules, but there is something else in the capsules that I had to filtrate out. I have documented this method here: http://www.mikrohamburg.de/Programm/Pro ... 170917.pdf
This will be a very soft tratment for the diatoms.
Started reading - very interesting! BTW, have you considered trypsin?
There are two types of EDTA, they are better soluble in water with somewhat higher pH value.
I think that the disodium EDTA salt is the appropriate one. It is used as 0.1M solution in 2% SDS in water.
These ovens were in use for enamel hobby work in the 1970s and can be bought here in Germany used for ca. 50-100€.
Will check on it.

I thought about an even simpler method: A stainless steel disc of 30mm diameter and 4-5mm thickness with a hole from the side to fit a temperature feeler in it. The temperature feeler would be grip and thermometer at the same time:
https://www.ebay.de/itm/LCD-Display-Typ ... 2129ba1d95
My temperature feeler didn't last long though used at 900°C.
Glass quickly becomes softer at over 500 °C so the temperature has to be limited.
Mine are epiphytic, not benthic right now, so I imagine 500C might be fine, no need of 900C.
Heating a cover slip with fresh diatoms with an alcohol or gas burner to 500 °C leads to oxidation of the organic material. Salt could be removed afterwards with water, lime with EDTA or vinegar concentrate. The diatoms stick to the cover slip and colonies stay attatched. It is a quick way to get slides that are nice to look at but not as sterile clean as the H2O2 and acid process.
Will send a PM about this.
There are electric kitchen ovens that clean themselves by heating to about 450 °C. These are probably also usable for diatom cleaning.
Mine goes up to 250C only, I am afraid.
Since the old processes with concentrated acids are not suitable for most hobbyists it is very worthwhile to look for alternatives. If they result in an acceptable permantent slide with not too much effort most hobbyists will be perfectly happy with the result.
Hopefully.

edit: sorry about the question about trypsin, just seen that pancreatin includes trypsin.
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Re: Thoughts about diatom cleaning

#11 Post by zzffnn » Sun Apr 29, 2018 12:16 am

MicroBob wrote:........
What I have tried with some success is pancreatin, ground pankreas from pigs. It is sold as medicine in gelantine capsules, but there is something else in the capsules that I had to filtrate out. I have documented this method here: http://www.mikrohamburg.de/Programm/Pro ... 170917.pdf
This will be a very soft tratment for the diatoms.
Bob,

That enzymatic digestion method makes sense, especially when there is lots of protein material to be removed. How does it work with fibers/polysaccharides though (I am guessing fibers are mostly broken down by mechanical forces and gut bacteria)? Do you have a typical result photo made by pancreatin that you can show us? Sorry, I am not smart enough read the language used for your article (German?).

The "something else in the capsules" are bulking agents (fillers) used to distribute active compound (pancreatin) and to make them more stable. They will interfere with your results and should indeed be removed. Likewise, if one solubilizes medication pills/capsules like vitamin C or aspirin for polarization microscopy, filtration is needed to remove those bulking agents for clean images.

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Re: Thoughts about diatom cleaning

#12 Post by Hobbyst46 » Sun Apr 29, 2018 9:59 am

zzffnn wrote: The "something else in the capsules" are bulking agents (fillers) used to distribute active compound (pancreatin) and to make them more stable. They will interfere with your results and should indeed be removed. Likewise, if one solubilizes medication pills/capsules like vitamin C or aspirin for polarization microscopy, filtration is needed to remove those bulking agents for clean images.
Thanks zzffnn for this important reminder.
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Re: Thoughts about diatom cleaning

#13 Post by MicroBob » Sun Apr 29, 2018 5:13 pm

Hobbyst46 wrote:BTW, have you considered trypsin?
Thank you for this input! Ground pankreas prbably contains much stuff I don't need and want, so it would be best to use the enzymes in pure form. I googles for trypsin and it is available at big chemistry dealers but probably difficult and expensiv to obtain. Over our society it can obain pretty much every chemical the is if I can name a reason, but I try to stick to widely available substances so my work can be repeated be othery without this privilege. Chemicals are difficult to obtain in Germany - I once ordered some precision metal weights for work and was asked to have a form filled out by the CEO that we won't use them to build bombs! :lol:

I would like to try enzymes that are used in dishwasher detergent but have not yet found a good source for them.



Mine are epiphytic, not benthic right now, so I imagine 500C might be fine, no need of 900C.
[Glass is somewhat soft at room temperature and becomes increasingly softer at higher temperatures, especially above 500°C. I'm not sure whether diatom frustules don't behave the same so I wouldn't use more than 500°C without further testing.
Mine goes up to 250C only, I am afraid.
The ovens I talked about are used up to ca. 250°C to prepare food and have a separate cleaning setting with 450 °C . This is probably only available in quite expensive ovens. We have a low tech gas oven without such a feature but with much better efficiency.

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Re: Thoughts about diatom cleaning

#14 Post by MicroBob » Sun Apr 29, 2018 5:20 pm

@zzffnn: Thank you for the hint with the bulking agent! Do you have an idea what chemical this is? I try to post images from the two processes I mentioned.

I found this bulking agent when my diatom sample increased in volume after the use of Pankreatin. :lol:
Under the microscope it looked like sand particles.

My document is written in german. Maybe google translator will help you understand the interesting parts of the text.

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Re: Thoughts about diatom cleaning

#15 Post by Hobbyst46 » Sun Apr 29, 2018 5:44 pm

MicroBob wrote:@zzffnn: Thank you for the hint with the bulking agent! Do you have an idea what chemical this is? I try to post images from the two processes I mentioned.
I found this bulking agent when my diatom sample increased in volume after the use of Pankreatin. :lol:
Under the microscope it looked like sand particles
In some pills, calcium carbonate it used as filler.
My document is written in german. Maybe google translator will help you understand the interesting parts of the text.
I have already translated it, or most of it, but Dr. G. Translator is not fluent in science (IMO) so I must format it somewhat. I can submit the translated text to the author, for approval then publication.
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Re: Thoughts about diatom cleaning

#16 Post by zzffnn » Sun Apr 29, 2018 5:46 pm

MicroBob wrote:@zzffnn: Thank you for the hint with the bulking agent! Do you have an idea what chemical this is? I try to post images from the two processes I mentioned.

I found this bulking agent when my diatom sample increased in volume after the use of Pankreatin. :lol:
Under the microscope it looked like sand particles.

My document is written in german. Maybe google translator will help you understand the interesting parts of the text.
Bob,

It should be stated on the medication bottle. With my calcium (carbonate) supplement pills, it seems to be the second listed ingredient "Croscarmellose Sodium".

There are many types of bulking agents, depending on active ingredient chemistry (and its interaction with bulking agent), manufacturing process and many other factors. It is cellulose type of polymer, usually.

In a pill/capsule, there are quote a few other agents, such as glue, agents that change taste and color, wetting agent, detergent, agents that texture and hardness.

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Re: Thoughts about diatom cleaning

#17 Post by desertrat » Sun Apr 29, 2018 6:01 pm

Sometimes interesting things show up on Ebay. This listing probably won't be much use to anyone outside the U.S., but it appears to be a pure product for laboratory use:

https://www.ebay.com/itm/Pancreatin-fro ... SwEW9aV9ay

I think I bought something from this seller before and there weren't any problems.
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Re: Thoughts about diatom cleaning

#18 Post by Hobbyst46 » Sun Apr 29, 2018 6:35 pm

@Rick: Thanks, yes! this is the better stuff, free from flavors and fillers. They only sell within the USA though. Will look for it elsewhere.
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Re: Thoughts about diatom cleaning

#19 Post by MicroBob » Sun Apr 29, 2018 8:55 pm

Hi Rick, thank you for posting the link! Pancreatin is actually sold by big chemistry dealers, but so far I only found it in big expensive amounts. They probably don't ship to Germany but the price would be very good.

I now found an enzymatic cleaner that contains several enzymes. I will try it and report the results.

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Re: Thoughts about diatom cleaning

#20 Post by MicroBob » Mon Apr 30, 2018 6:12 pm

Hi together,
here I show some pictures of a diatom slide, cleaned with pancreatin and EDTA. The sample is from Kraterquelle Bad Nenndorf where you find amphipleura pellucida the whole year round. I can't remember whether this was before or after I found out about the bulking agents in the pancreatin. :roll:

For me the diatoms are cleaned very well but the frustules are not always divided in two. There is enough dirt and bubbles in the slide left to prove it is an original. Some of the dirt is probably also not removable with strong acids. Some might be from the bulking agent. Some of the dirt is in the light path too.

My impression was that there has to be an easier way to get enzymes to work than with pancreatin. I'm witing to see how the enzyme cleaner works that I have ordered yesterday. It's quite special stuff and probably not available further away from Germany.

Bob
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Re: Thoughts about diatom cleaning

#21 Post by Hobbyst46 » Mon Apr 30, 2018 6:49 pm

Hi Bob
Questions:
Are they benthic diatoms?
how were they collected?

Certain components of "dirt" are resistant against HCl, H2SO4, HNO3. As mentioned in the presentation of your group meeting - use physical, not chemical methods in such cases.
Incidentally, seople have devised some sophisticated methods of physical separation, but they are complex and require special equipment - pumps, flow troughs etc.
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Re: Thoughts about diatom cleaning

#22 Post by MicroBob » Mon Apr 30, 2018 6:56 pm

They are from fresh water, a water basin near a crater near Hannover.
I got the sample in a bottle by mail and don't know how he took it.

The amphipleura pellucida is very difficult to see. So this was more about microscope technics than biology.

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Re: Thoughts about diatom cleaning

#23 Post by desertrat » Mon Apr 30, 2018 7:01 pm

For members who are having trouble finding pancreatin outside of the USA, Electron Microscopy Sciences has two listings for Trypsin on the following page:

https://www.emsdiasum.com/microscopy/pr ... annic.aspx

The company also has outlets in many countries overseas. The home company here in the US sells their products to individuals, but I don't know if the overseas partners will. See below.

https://www.emsdiasum.com/microscopy/orders/agents.aspx
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Re: Thoughts about diatom cleaning

#24 Post by Hobbyst46 » Mon Apr 30, 2018 7:15 pm

Thanks @desertrat - I will contact their local salesperson. Great!
Yet the safety data sheet claims that solid trypsin is a class 2 eye irritant and that it is 1:100 powder. What substance is the 99 - could not find. Anyway, an eye irritant powder does not sound pleasant outside of a proper lab. We will see...
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Re: Thoughts about diatom cleaning

#25 Post by desertrat » Mon Apr 30, 2018 7:46 pm

I visited Klaus Kemp's diatom site, because I thought I remembered seeing some material on cleaning diatoms. Mr. Kemp has hosted the Amateur Diatomist periodical. Out of curiosity I opened the most recently uploaded page.

Scrolling down, there is an article on cleaning diatoms without chemicals. It seems beautiful in its simplicity.

A cover slip is placed on a steel plate. A drop or two of water rich in diatoms is placed on the cover slip. A "blowtorch" is lit. I'm guessing the hand held propane torches found in hardware stores should work. The flame is played cautiously on the diatom mixture until it is dry. Further careful heating turns the living matter inside the frustules into carbon. Still further careful heating causes some unreacted oxygen carried to the diatoms by the flame to oxidize the carbon into carbon dioxide which escapes through the diatom pores.

Result is clean diatoms. If I was going to do this, I would probably put the steel plate on a fire brick or similar refractory material.

For what it's worth.

http://www.diatoms.co.uk/ad/vol6pt1.htm
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Re: Thoughts about diatom cleaning

#26 Post by Hobbyst46 » Mon Apr 30, 2018 8:15 pm

desertrat wrote:A cover slip is placed on a steel plate. A drop or two of water rich in diatoms is placed on the cover slip. A "blowtorch" is lit. I'm guessing the hand held propane torches found in hardware stores should work. The flame is played cautiously on the diatom mixture until it is dry. Further careful heating turns the living matter inside the frustules into carbon. Still further careful heating causes some unreacted oxygen carried to the diatoms by the flame to oxidize the carbon into carbon dioxide which escapes through the diatom pores.
Yes, this incineration method has been mentioned by members of this forum who discussed the details. And it is really appealing, but the temperature must be controlled, otherwise the cover-slip (and diatoms...) will be damaged by the heat. It is on my to do list.
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Re: Thoughts about diatom cleaning

#27 Post by desertrat » Mon Apr 30, 2018 8:35 pm

Yes, I think it would take some practice to get good results with the torch.

RE: the trypsin product listing, the item below the 1:100 powder listing describes the enzyme as concentrated, but it is quite costly for a small amount. I think any of these powerful digestive enzymes would be skin and eye irritants, after all they digest proteins!

It seems any chemical method of removing the living matter from the frustule would involve products that will eat the skin off one's fingers.
Rick

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KurtM
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Re: Thoughts about diatom cleaning

#28 Post by KurtM » Tue May 01, 2018 1:48 am

I've had incineration on my list of things to try for about 5 or 6 hundred years now, but still haven't gotten around to it. If any of you try it, please do post a report!
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billbillt
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Re: Thoughts about diatom cleaning

#29 Post by billbillt » Tue May 01, 2018 6:12 am

Hobbyst46 wrote:
desertrat wrote:A cover slip is placed on a steel plate. A drop or two of water rich in diatoms is placed on the cover slip. A "blowtorch" is lit. I'm guessing the hand held propane torches found in hardware stores should work. The flame is played cautiously on the diatom mixture until it is dry. Further careful heating turns the living matter inside the frustules into carbon. Still further careful heating causes some unreacted oxygen carried to the diatoms by the flame to oxidize the carbon into carbon dioxide which escapes through the diatom pores.
Yes, this incineration method has been mentioned by members of this forum who discussed the details. And it is really appealing, but the temperature must be controlled, otherwise the cover-slip (and diatoms...) will be damaged by the heat. It is on my to do list.
How about this method using a hotplate?..

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Re: Thoughts about diatom cleaning

#30 Post by MicroBob » Tue May 01, 2018 8:15 am

A hotplate that has a very even surface and reaches 500°C would be perfect. Glass is already fairly soft at 500 °C and has to be well supported from below.

I have tried a cover slip holder bent from thin stainless in combination with a propane torch. Here the cover slip tended to move, some diatoms were blown away and some coverslips were bent due to a lack of heat control.

I have tried a piece of 4 x 6 cm 4mm stainless over a small alcohol burner. I had the impression that I didn't reach a high enough temperature. A member of our group reported that she used a travel cloth iron for this purpose, but I think few cloth irons reach a high enough temperature.

A car cigarette lighter might be a good heat source with a 4-5mm even stainless steel (silver, platin...) disc on top.

I think it would be nice to lead a slow stream of oxygen onto the cover slip or add an oxidizing agent to the process.

These thermostats should be able to offer a controlled electric heating: https://www.ebay.de/itm/Inkbird-ITC-100 ... SwUKxYmppI

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