Biddulphia diatom from norther Atlantic plancton

[MicroBob]

Hi together,
I ran another stack of images through PICOLAY.
Here a Biddulphia, probably Biddulphia baileyii. If you can support or correct this ID I would thank you.

The sample was cleaned at ca. 450°C for 30 minutes to avoid deformation. The pictured diatoms so far don't seem to have suffered and would probably withstand quite a bit more fire.
Image is stacked, sharp details are not in one plane!

Bob

[Hobbyst46]

Another very nice image, Bob.
I would hesitate to prolong the incineration or increase the temperature. I am afraid that the four thin long protrusions are already on the verge of bending.

[75RR]

Nice work!

Given the side protrusions and the length of the corner ones I would suggest Biddulphia granulata as a possible ID. https://botany.natur.cuni.cz/algo/database/node/722

[MicroBob]

Hi Doron,
you might be actually right. The lower left spine has a fine S-shape that doesn't look like naturally grown this way.
Unfortuately I have never read about any detailed tests about diatom incineration and deformation resistance of certain species of diatoms. It was your own tests that made me aware of the problem of deformation. Overall I'm quite happy with the result. Little work, acceptable cleaning, diatom halves and girdle bands in place, acceptable amount of deformation. What I didn't find in the slide that was visible before: Very nice view of the interconnection of Biddulphia diatom chains. They don't look that great after cleaning.
BTW: I have just finished building a nice little variable electric hot plate. It contains a 40W heat element from a 3D printer and a K-type thermocouple in a lillte aluminium block. The block is coupled to the base by menas of an 4 pol XLR plug, so it can be exchanged. So far I used it for Pleurax mounting, but with a smaller and better insulated block it might be usable for incinerating too. Do you think a supply of oxygen could speed up the cleanin process? Since little volume is needed this could be generated by electrolysis on the go.

Bob

[MicroBob]

Hi Glen,
thank you, you are probably right, at least closer than I was: https://botany.natur.cuni.cz/algo/database/node/725

So it proably is a Biddulphia granulata

Bob

[Hobbyst46]

BTW: ...I have just finished building a nice little variable electric hot plate. It contains a 40W heat element from a 3D printer and a K-type thermocouple in a lillte aluminium block. The block is coupled to the base by menas of an 4 pol XLR plug, so it can be exchanged. So far I used it for Pleurax mounting, but with a smaller and better insulated block it might be usable for incinerating too. Do you think a supply of oxygen could speed up the cleanin process? Since little volume is needed this could be generated by electrolysis on the go....

1. I hope and trust that the heat element is secured to the aluminum block, since if it is, by accident, separated from the block, and given its small heat capacity, it might overheat in seconds (this is my experience with 6mm diameter finger-like heating elements) and become damaged.
2. I believe that yes, adding oxygen will speed up the process. However, I would not "simply" supply oxygen to a hot aluminum piece without careful study of the literature data about the ignition point of aluminum. Aluminum is less reactive than magnesium, but in an atmosphere of oxygen at several hundred degrees - I am not at all sure that it is safe.

[MicroBob]

Hi Doron,
these heat elements are also a bit dangerous as they can heat up to a temperature that can easily ignite things around them. They should sit in a hole with thermal compound and be pressd to one wall there by a screw from the side. To make shure it can't slip out there should be a second screw that blocks the exit path. A couple of 3D printers have started to burn because there was only one screw to hold the heat element in by force from the side. When the block is small it can also heat up to dangerous temperatures so the thermocouple mustn't slide out too.
When I find the time I can show the little universal hot plate here and point out the safety aspects.
With the "aluminium fire bomb" you are right. Since it is probably difficult to define what is safe and what not it will probably be better to use a ceramic base for the hot plate in this case.

Bob

[Hobbyst46]

these heat elements are also a bit dangerous as they can heat up to a temperature that can easily ignite things around them. They should sit in a hole with thermal compound and be pressd to one wall there by a screw from the side. To make shure it can't slip out there should be a second screw that blocks the exit path. A couple of 3D printers have started to burn because there was only one screw to hold the heat element in by force from the side. When the block is small it can also heat up to dangerous temperatures so the thermocouple mustn't slide out too.

Exactly my thoughts and preferred method! thinking alike...

Diatom cleaning by Incineration seems to be a weapon in the hands of hobbyists, rather than researchers. I often ponder about incineration, since its potential advantage relative to chemical cleaning is obvious. Why do they deform ? does the "glass" soften or even melt ? man-made glass does not soften at 450C. Perhaps the diatom frustule includes some organic residues as part of the silica structures, and when this residues are destroyed by the heat, the silicate structure is deformed. On the other hand, if that was true, then strong boiling oxydizing acids would have caused the same result, namely, frustule bending and deformation, contrary to what I know from publications. Do you know of any direct comparison between acid digestion and incineration on the same type of diatoms ?

[MicroBob]

the incineration method has been used by several people and the scientific merit of it has just recently been pointed out by an experienced older member of our group. So I don't really know whether the choice of cleaning method divides precisely between amateur and researcher.
With diatoms it has been quite special: There were many professionals who worked for a profit, and not as a researcher at an university or so. Albert Elger and Johann Dietrich Möller were diatom slide preparators by profession. Friedrich Hustedt was a teacher and school director. Generally many slides were made for the enjoyment of their beauty and not for scientific purposes, Maybe this has influenced the ideal how diatom slides are expected to look. I have never seen a direct comparison of incineration and hard chemical cleaning methods so far.

Glass is defined as deep cooled fluid. It is not crystallized. I found a nice chart that shows the viscosity over the temperature: https://www.hindawi.com/journals/acmp/2008/817829/fig4/
It is fairly ridgid at room temperature but gradually softens as it is heated, as does the cover slip, usually made from borosilikate glass. I was not able to find information whether diatoms show a similar behaviour.
In SEM images diatoms often look very porous. I was told that this is even the case in material that has been cleaned by H2O2 only. These pores might be there in the live diatom, or they are filled with something that can be resolved by H2O2. When looking at cleaned diatoms it is visible that some are built strongly and others are very delicate. Also the available substances to inclue into the SiO2 material will be very different depending on the environmental conditions. It would be nice to be able to predict which diatoms will suffer from incineration.

Bob

[Hobbyst46]

Thanks for the link, Bob. The diagram indicates that even the cheapest and softest glass, soda lime glass, softens only at 650-700C. Must read and learn more about the reason for difference between man-made glass and frustule "glass".

[MicroBob]

My interpretation is different: It already moves at room temperature, but takes ages. For glass this is a non-linear function of time and temperature, starting below room temperature. With diatoms there might be an additional effect added due to unhomogenous material. Depending on how this material reacts strong forces can start to work on the diatom structure. This wouldn't be too difficult to research but it still is probably not generally available knowledge so far. I often get the impression that we happily destroy a nature that we just have begun to discover...