Microscopy – Pleurosigma balticum by Smith, Beck and Beck

Some of the microscope slides I get are quite expensive, either rare examples, unusual mounts, or sought after makers. Others however are not. Today’s post is one with slides of the latter. I got two slides by Smith, Beck and Beck, and for the pair they cost me the princely sum of £5 (plus £3.50 postage). As it turned out, one of them was pretty much useless – degradation over time – but the other still had some good diatoms on it.

The images as per usual were done on my modified Olympus BHB, this time using 450nm oblique illumination. The 40x images used a Nikon UV-F NA 1.3 objective with glycerine immersion. Photoeyepiece was a Nikon 5x CF. Camera was a monochrome converted Nikon d800. Image resolution reduced to 1600 pixels across for sharing here.

Here is a stack of 10 images from the slide described as ‘Pleurosigma balticum’.

40x image of the P. balticum slide

As well as there being plenty of P. balticum, there are various other diatoms on the slide including quite a few Surirella gemma. Quite a few of the examples have degraded somewhat, but there are still some usable ones on there. Most of the detail in the image above will be lost because of reducing the size for sharing, but the crop below is at original resolution.

Crop from 40x image at original resolution

As can be seen from the crop, there is plenty of detail in the P. balticum diatom.

A wide field of view using a 10x objective shows how more of the slide looked showing the variation and density of the slide.

Wide field of view of the P. balticum slide with 10x objective

Unfortunately the other slide, marked P. quadratum, was pretty much unusable (10x objective image below).

Wide field of view of the P. quadratum slide with 10x objective

And of course, here are the slides themselves.

Two Smith, Beck and Beck slides

At first glance the slides look similar, but the printing and importantly the addresses are different. They were at 6 Coleman Street from 1847-1856, while at 31 Cornhill from 1865-1880 (according to Bracegirdle’s ‘Microscopical Mounts and Mounters’) which makes these some of the older slides that I have, especially the P. quadratum one. Last week I spent £5.40 at a service station for a sandwich while visiting the Archives of the Science Museum near Swindon to go through documents by Horace Dall (more on that soon after I have gone through my notes), so for less than my sandwich I got a nice slide to examine.

As always, thanks for reading, and if you’d like to know more about my work, i can be reached here.

UV Microscopy – Cymatopleura elliptica diatom slide by Klaus Kemp using 365nm light

A few days ago I took a look at a Klaus Kemp slide of diatoms called Cymatopleura elliptica with 450nm light and a Leitz 63x Pl Apo NA 1.4 objective and, well, the image was not as good as I had hoped. Today I decided to revisit the slide with a different approach, and this post shows the results of that work. The image was done on my modified Olympus BHB microscope, light source was a Zeiss Mercury Xenon lamp. Objective was a Leitz 100x Pl Apo NA 1.32-0.60 (oil immersion). Condenser was a Watson Holoscopic one (again with oil). Objective iris was closed down slightly with the aim of trying to produce circular oblique lighting (COL). Photoeyepiece was a Nikon 5x CF. Filters – 365nm (10nm bandpass, Edmund Optics, 2 stacked together), 405nm (10nm bandpass) and 450nm (40nm bandpass) from Thorlabs. Camera – monochrome converted Nikon d800 from MaxMax. At 365nm, a stack of 18 images processed in Zerene stacker. Image cropped slightly and reduced in resolution for sharing. The camera produces slight colour casts and I have kept those here as I like the effect. And after all that, here it is.

Cymatopleura elliptica from Klaus Kemp slide, 365nm light, Leitz 100x Pl Apo objective

Moving to 365nm light produced a noticeable improvement in resolution, although that is probably lost a little on the image above which is 1600 pixels across compared with the original (5826 pixels across). As an example of the resolution of the original, the image below is a crop before it was reduced in size.

Cymatopleura elliptica from Klaus Kemp slide, 365nm light, Leitz 100x Pl Apo objective, cropped

There is plenty of detail in the image, much more than my initial attempt with 450nm light. Going in closer and checking in ImageJ, some of those features are about 280nm apart.

ImageJ showing two features 281nm apart (0.281 microns)

While the slide was on the microscope I took a series of 3 images of it at 3 different wavelengths (365nm, 405nm and 450nm). These are shown below.

Diatom features at 3 different illuminant wavelengths, 365nm (left), 405nm (middle) and 450nm (right)

The images above are unprocessed and not sharpened, but the microscope was refocused each time. It demonstrates nicely how the shorter wavelength light brings out the features in more detail (as expected by Abbe).

The slide actually has 4 examples of the diatom on it. The larger one was the one that was imaged.

4 diatoms on the slide

It looks as though there may something unusual with the fixative, as shown by the droplets in the image which were very visible on this slide. These were not on the outside of the slide or coverslip. Here’s the slide.

Cymatopleura elliptica slide by Klaus Kemp

The mountant is Hyrax which was one reason I decided to try 365nm light (it has pretty good UV transmission at 365nm). What was more surprising was the objective – I expected the Leitz 100x Pl Apo to block a lot of the UV and it actually performed really well. I must remember this for future work. Diatom naming is still well beyond me, but this one is also sometimes referred to as Surirella undulata (see here).

UV microscopy presents its fair share of challenges, but imaging at 365nm is the more straightforward end of the spectrum to try and provides some quite visible improvement in resolution compared with visible light. Be safe though if you plan on trying this – I use UV safety specs whenever dealing with UV light sources. As always, thanks for reading, and if you’d like to know more about my work I can be reached here.

Microscopy – Actinoptychus heliopelta from Eric Impey slide

A couple of weeks ago I had a box of assorted slides come through which have turned out to have some real gems in it (I shared some initial images here). Today’s post looks at another slide from the box – an Actinoptychus heliopelta by Eric Impey from 1970. Images were done on my modified Olympus BHB microscope using 450nm light (slightly oblique). The objective for the main image was a Leitz 63x Pl Apo NA 1.4 which recently arrived from JB Microscopes. A Nikon CF 5x photoeyepiece was used. 27 images were stacked in Zerene. Images have been reduced in resolution for sharing.

Here’s the main image.

Actinoptychus heliopelta from a slide by Eric Impey. Leitz 63x Pl Apo NA 1.4 objective

The sample is beautiful and there is plenty of detail on there, some of which is lost on here as I had to reduce the resolution for sharing. Below is part of the image shown at the original resolution.

Crop from the main image, shown at original resolution

The slide itself has 3 examples of the diatom on it, shown below (single image, not stacked, using a Nikon 20x Plan Apo objective). The one in the main image is actually the one on the right hand side of the image below.

3 diatoms from the Eric Impey slide

And the slide itself. The diatoms came from Dunkrik, Maryland. The mount is Naphrax, and it is a very well made slide, which even has a slightly decorative ringing around the coverslip.

Eric Impey slide of Actinoptychus heliopelta

As an aside, I think I have spent too much time looking at diatoms this weekend. This was what I saw when I looked down inside a plastic coke bottle…..

Coke bottle model of a diatom

Before I go, being an equipment geek, I’ll also share the objective as I was very impressed by the quality of the image it produced. It’s a Leitz 63x Pl Apo NA 1.4, oil immersion. Here it is alongside it’s big(ger) brother, the 100x with an adjustable iris, which is also an excellent performer.

Leitz 63x and 100x Pl Apo objectives

At the risk of sounding like a broken record, I continue to be amazed by the quality of some of these older slides, and would well recommend them for anyone interested in looking for samples to image. This slide cost me all of £5.50 plus postage. If you don’t want to buy slides but relish new slides to look at, the Postal Microscopical Society offers members the chance to borrow slides from their collection and is well worth checking out. Thanks for reading and if you’d like to know more about this or other aspects of my work I can be reached here.

UV Microscopy – Pleurosigma angulatum diatoms by Horace Dall, with a Nikon 40x UV-F objective

Today’s post has come about as the result of a chat with a microscope shop who I use to check over my objectives when they need fixing (JB Microscopes Ltd in Newcastle). A few weeks ago I bought an 20x Olympus Splan Apo that had some optical issues (the price was right and I had hoped it was worth the gamble). To see if it could be saved I sent it to JB Microscopes to be looked over and hopefully fixed. Unfortunately it could not, but while I was chatting with them I asked what objectives they had on their shelves. It turned out that they had a couple that I had been looking for for a while – a Nikon 40x UV-F glycerine immersion objective, and a Leitz 63x Pl Apo oil immersion objective. This post will cover some initial results with the Nikon 40x UV-F.

For the image I used an aluminium coated slide by Horace Dall. The slide is marked PA indicating it as Pleurosigma angulatum diatoms. Imaging was done on my modified Olympus BHB using 365nm light from an LED torch, an Olympus Abbe condenser (glycerine immersion), the Nikon 40x UV-F NA 1.30 objective with glycerine immersion, and a Nikon 5x CF photoeyepiece. Light was filtered with an Edmund Optics 365nm, 10nm bandpass filter. Camera was a monochrome converted Nikon d800 by MaxMax. 8 images were stacked in Zerene. The main image has been reduced in resolution for sharing.

Dall slide image using the Nikon 40x UV-F glycerine immersion objective

The final image was about 6200 pixels across and has been reduced to 1600 here. The stack produced plenty of detail, and to try and show this better, there are a couple of crops below which are shown at original pixel resolution.

Crop at original pixel resolution
Crop at original pixel resolution

And of course, here’s a photo of the amazing Horace Dall slide.

Aluminium coated Horace Dall slide

What about the objective? Here it is.

Nikon 40x UV-F NA 1.30 glycerine immersion objective
Nikon 40x UV-F NA 1.30 glycerine immersion objective

Why is this a special objective? Firstly, it’s a 40x objective with high NA. It is also quite rare, dating to around the mid to late 1980s. Originally developed for fluorescence imaging work, so it has good UV transmission (for longer wavelength 365nm UV anyway). There’s not much info about these objectives out there, but Charles Kreb’s site shows a Nikon CF brochure which has the 100x version of the objective, here. These aren’t Plan objectives nor are they Apo, so expect some field curvature and chromatic aberration if not using monochromatic light. What they are designed for is the let a lot of light through, and they certainly do that.

I have a 100x version of the objective, which has also been used for imaging at 365nm. The 100x is nice as it has an adjustable iris making it great for darkfield. Here are the 40x and 100x together.

Nikon 40x and 100x UV-F objectives

If anyone has the 10x and 20x from this series that you are looking to sell, please let me know as I am on the lookout for those two for my UV work.

We often do not thank our suppliers, but they make the work we do possible. As such, thanks again to JB Microscopes – great customer service and worth contacting if you are in need of something specific (they do not list their stock on their site). As always, thanks for reading, and if you’d like to know more about my work, I can be reached here.

Microscopy – images from the latest slide box

Occasionally I’ll buy a little bit of a ‘lucky dip’ selection of slides to image on the microscope, especially if the same seller has a number of them for sale at the same time. At the weekend a box of 8 slides came through, and I wanted to share some of the images from a few of the slides. Images were done on my Olympus BHB microscope and have been reduced in resolution for sharing here.

First is a diatom slide, an Actinoptychus hexagonus by W.A. Firth, imaged using a 60x Olympus Splan Apo NA 1.4 objective with oblique 450nm illumination.

Actinoptychus hexagonus using a 60x objective

Lots of lovely detail in the 60x image (this was a stack of 24 images). There are actually 2 diatoms on the slide, and here’s what they look like together, using a 10x objective and oblique light.

10x objective image

The main 60x image was of the one of the right. Here’s the slide itself.

W.A. Firth slide of Actinoptychus hexagonus

Next is another diatom slide, this time a strew from Oamaru. I only have a very preliminary image of one of the diatoms I found on this, as I then went on the Diatom Images facebook page to get an ID for it (I’d not seen one before). It is apparently Brightwellia coronata. Single image with a 20x objective.

Brightwellia coronata from an Oamaru strew slide

Finally for now, something a bit different – Salicine crystals imaged using cross polarized light and 4x Zeiss Planapo objective.

Salicine with a 4x objective and cross polarized
Salicine with a 4x objective and cross polarized
Salicine with a 4x objective and cross polarized

And the slide itself.

Salicine slide

There’s a few more in the box to look at….

Slide box to check out

This box of slides cost me about £8 per slide including delivery, and will certainly give me plenty of enjoyment with trying to image them. I’m a huge advocate of second hand and older slides, and they are well worth checking out.

As always, thanks for reading, and if you’d like to know more about my work, i can be reached here.

Microscopy – Horace Dall Soldier Beetle slide in visible and IR light

For those who frequent my blog, you’ll have heard of the slide maker Horace Dall before. I’ve been a keen collector of his metal and metal oxide coated diatom slides for a while (and am currently writing an article on them which I hope to publish later this year). I recently came across a slide of his for sale which was a bit different though – not a diatom slide but a whole Soldier Beetle. Today I’ll share some images from this slide using both visible light and Infrared (IR).

With diatoms, I normally have to go to high magnification to see them. However with this slide the problem I had was going to a low enough magnification, as the whole sample is about 20mm across. To image the whole beetle, I took 4 images using a 1x Olympus Splan Fl objective and stitched them together in Photoshop. Here’s what the sample looks like (resolution has been dropped from the original 9390×10687 to 1600×1821 for sharing).

Horace Dall Soldier Beetle slide. Composite of 4 images using a 1x Olympus Splan Fl objective

A higher magnification image of the head of the beetle using a 4x Zeiss Planapo objective.

4x Zeiss Planapo image of the head of the Soldier Beetle

And to finish with a couple of images using a 10x Olympus UVFL objective.

10x Olympus UVFL objective image of the Soldier Beetle head
10x Olympus UVFL image of part of the wing and leg of the Soldier Beetle

While chatting with a friend on a microscopy forum he mentioned to me that IR light can be useful for imaging insect microscope slides as it makes some parts become more transparent. To try this out I swapped the LED light source for a Tungsten bulb, and placed a Heliopan 780nm long pass filter over the field lens, and then imaged the slide again.

Here’s the composite of 4 images using IR light (the IR images have a slight pink tinge in the JPEG for straight from the camera).

Horace Dall Soldier Beetle slide. Composite of 4 images using a 1x Olympus Splan Fl objective and using IR light

The IR light does indeed make parts of the insect appear more transparent, and the overall effect is to produce a lower contrast image. Next up the head using the 4x Zeiss Planapo objective.

4x Zeiss Planapo image of the head of the Soldier Beetle using IR light

Again, the increased transparency if obvious. Finally some images using the 10x Olympus UVFL objective.

10x Olympus UVFL objective image of the Soldier Beetle head using IR light
10x Olympus UVFL image of part of the wing and leg of the Soldier Beetle using IR light
10x Olympus UVFL image of the eye of the Soldier Beetle using IR light

I did an additional image here of the eye with the 10x objective. The IR cuts through the darkly pigmented area and shows more of the structure of the eye. I think I need to come back to this with a higher magnification and try a stack. The 10x objective has a bit of a hotspot in the middle of the image in the IR photos. This behavior is often seen in IR photography when the lenses aren’t suitable for IR, and I presume that is the case here.

As a final set of images, I thought I would try imaging the eye region in IR with a 20x objective (a 20x Nikon Plan Apo NA 0.65). 3 different images are shown here; a single image at a given focus point (bright field), a stack of 4 images (bright field), and a single image using oblique bright field. These images were desaturated to remove the pink tinge from the IR images.

20x objective, single image, bright field, IR
20x objective, stack of 4 images, bright field, IR
20x objective, single image, oblique bright field, IR

The single image using the 20x objective shows a surprising amount of detail especially in the surface of the eye. The stack of 4 images shows even more detail and some of the tubular structures of the eye lens elements. The oblique image is more of a cross section through part of the eye but does nicely highlight the structure of the individual lens elements. Interestingly this 20x Nikon Plan Apo seems to have very little hotspot in the IR so could be a good one to use again in future.

As per usual here’s an image of the slide as well.

Soldier Beetle slide by Horace Dall

Every now and then it is nice to have a break from imaging diatoms and look at a different sample. By moving from visible light to IR it was possible to seem through some of the dark areas of the beetle’s structure. Thanks for reading, and if you’d like to know more about my work I can be reached here.

Photography – Infrared imaging with the Zeiss ZF-IR 25mm and 50mm lenses

While most of my imaging outside of the visible spectrum is in the Ultraviolet, I do also like to take photographs at the long wavelength end in the Infrared (IR), especially for landscapes. Many lenses suffer from hotspots when used in the IR adding complexity when processing images. A few years ago Zeiss released their ZF-IR lenses (25mm, 50mm and 85mm) which had coatings on them to produce better IR transmission and reduce hotspots. These lenses weren’t available for long before Zeiss stopped selling them and they have now reached something of a cult status making them hard to find (and expensive) second hand. I recently managed to source examples of the 25mm f2.8 and 50mm f1.4 ZF-IR lenses from the photography dealer Jo Geier at Mint and Rare in Austria, and today I wanted to share some initial thoughts on them.

I’ll come to the transmission through the lenses in a minute, but to start with a visual comparison of the front elements of the 25mm ZF-IR and a normal version of the lens the 25mm ZF.2. This shows the reflection of sunlight through my kitchen window.

Coating colour from the Zeiss 25mm ZF.2 (left) and ZF-IR (right)

The coating on the front elements is very different between the two lenses as can be seen by their colour. Couple of things to note here. Ideally I would compare the ZF-IR with the ZF version, but I happened to have a ZF.2 copy of the lens. The ZF.2 came after the ZF but I would think the coatings would be very similar as the main difference was the addition of electrical contacts for providing aperture data. Note I have blurred the last 2 digits of the serial numbers on the lenses.

I measured the transmission through the 3 lenses I have (Zeiss 25mm f2.8 and 50mm f1.4 ZF-IR and 25mm f2.8 ZF.2) using my Ocean Insight spectrometers and a couple of light sources – xenon and halogen lamp. This allowed me to measure transmission from 300nm to 1000nm, although as I will explain with a couple of caveats.

First the comparison between the 25mm ZF-IR and ZF.2 lenses.

Zeiss 25mm ZF-IR and ZF.2 transmission comparison

The ZF-IR transmission is lower at the blue end of the spectrum than the ZF.2 but while the ZF.2 transmission drops sharply above 700nm the ZF-IR does not. This matches what I’d expect to see from the Zeiss product data sheets. My system sensitivity drops sharply above about 920nm, which is why the data gets very noisy up there, and I don’t think the drops and peaks at around 950nm are real features. The curves are shown in 3 sections as I used 3 setups to measure them. Overall though the ZF-IR certainly offers better IR transmission above 700nm.

Now the Zeiss 50mm f1.5 ZF-IR and 25mm f2.8 ZF-IR.

Zeiss 25mm and 50mm ZF-IR transmission comparison

The Zeiss 25mm and 50mm ZF-IR have very similar shaped curves, which is what would be expected assuming they have the same coatings.

I did some quick landscape test shots with the 25mm f2.8 ZF-IR using my monochrome converted Nikon d800 camera from MaxMax and a Heliopan 780 IR filter, and these are show below.

The lens certainly seems to live up to its reputation for not producing hotspots in the IR. I have heard that the 50mm ZF-IR is more prone to hotspots, although I have not been able to replicate that yet. To finish with, a not often seen photo of the 25mm and 50mm ZF-IR lenses together.

Zeiss 25mm and 50mm ZF-IR lenses

Overall, I’m very happy with the two Zeiss ZF-IR lenses and they will be a great addition to my non-visible light imaging capability. As always, thanks for reading and if you’d like to know more about my work, I can be reached here.

Microscopy – Hydrosilicon mitra diatom slide by S.H. Meakin

I have an unusual (and rather rare) diatom slide to share with you today – an example of Hydrosilicon mitra, prepared by S.H. Meakin. This was made in 1933, and is mounted in Hyrax (which will become important later). The images shared were taken on my modified Olympus BHB microscope, with a monochrome converted Nikon d800 camera. The images have been reduced in resolution for sharing.

The first is a simple bright field image. This is a stack of 7 images and was done using 450nm filtered LED light. The objective was a 40x Olympus Dplan Apo UV (NA 0.85). Condenser was an Olympus Aplanat Achromat.

40x objective, bright field image

The sample is not flat, and dips towards one side. This means that stacking was necessary with the 40x objective (in fact I missed the focus on the top left of the diatom – ” ‘B-‘ must do better next time”). As can be seen there is some damage to the fine structure of the diatom, but it is still a very pretty specimen.

I wanted to see what this looked like with dark ground illumination, so I got out my Watson Holoscopic condenser (some info about that here) and used glycerine as the immersion fluid to attach it to the underside of the slide. The objective was a 20x Olympus Splan NA 0.46, and again 450nm light was used. No stacking this time, just a single image.

20x objective, dark ground image

I love the dark ground effect, but being a single image part of the diatom is out of focus due to it not being flat. I’ve not got my head around stacking dark ground images yet.

As a final image, I wanted to try something different. As mentioned above the mount is Hyrax, and this has pretty good UV transmission at 365nm. I wanted to try imaging with 365nm light (to potentially help improve resolution), and also use a different method of illumination – circular oblique light (COL), also known as annular illumination. To do this I used a 40x Olympus UVFL PL NA 1.3 silicone immersion objective in combination with the Watson Holoscopic condenser. This objective has an adjustable iris – wide open and the NA is bigger than that of the condenser and the image is bright field. Iris closed all the way down and the image becomes dark ground as the objective NA is now smaller than the condenser. In the middle ground COL can be produced, when the NA of the objective is close to that of the condenser. This gives a nice 3D effect to the image. Both the condenser and the objective were used with glycerine as the immersion fluid. The image below was a stack of 13 images, using 365nm LED light, and with a COL setup.

40x objective, COL illumination

COL illumination gives a more 3D effect to some of the features. But, and this is a big ‘but’, the resulting image was very noisy, and was a bit of a nightmare to stack. Not sure why it was so noisy, as I used ISO200 on the camera. I really like the end result though and will definitely try this technique again.

As always, here’s the slide itself as well.

Hydrosilicon mitra slide by S.H. Meakin

Not too bad for a slide made 90 years ago. The slide was bought on ebay for about £30 and there is a single example of the diatom on it. As always, thanks for reading, and if you’d like to know more about my work, I can be reached here.

Microscopy – cross polarized slide of acetate of strychnine

Today’s post shows some images of a slide of acetate of strychnine, made by John T Norman. Based on the available information I would date this to the late 1800s. Cross polarized lighting can be used to create wonderful coloured images of crystals, and I have used that technique here to image the crystals on the slide. Images taken using my modified Olympus BHB microscope and with a Canon Eos R7 camera. Objectives were a 1x Olympus Splan Fl and a 4x Zeiss Planapo. Images have been reduced in resolution for sharing.

1x objective
1x objective
4x objective
4x objective
4x objective
4x objective
4x objective

As always, I like to share an image of the slide itself, so here it is.

Acetate of strychnine slide by Norman

I find these cross polarized images of crystals absolutely fascinating, and I hope you do too. Thanks for reading, and if you’d like to know more about my work, I can be reached here.

Microscopy – Tasmanian rock with orange lichen

Earlier this year I picked up a rock with some orange lichen on it from a beach on the north west coast of Tasmania. I was interested to see how it looked under UV induced fluorescence and it did not disappoint (some initial fluorescence photos of it were shared here). A few weeks ago I came across an advert for someone who could make microscope slides of thin sections of rock (Dr Andrew Beard at Geology Hub) and I reached out to see if he would be able to make some thin sections of my Tasmanian rock sample so it could be viewed on the microscope. He was really helpful, and I sent him a few of my spare fused silica microscope slides (in case I wanted to try illuminating them with UV for fluorescence) and the rock sample and he made me a few slides to look at. Today’s post shared some initial images.

First a reminder, here’s the rock sample, front and back, in normal visible light and under UV induced fluorescence using 365nm light. It was about 3cm across and 1cm thick.

Front of the rock sample
Rear of the rock sample

The front surface had an orange lichen on it it which also fluoresced orange under illumination with 365nm light. The rear had a couple of areas (towards the top left of the image) in which the matrix of the rock looked to be fluorescing yellow under 356nm light. I asked Dr Beard to prepare a few slides of the rock showing 2 specific areas – the orange lichen and the yellow rock matrix fluorescence. For the microscopy images, I used my modified Olympus BHB microscope, an Olympus Abbe condenser, a 10x Olympus UVFL NA 0.4 objective, an Olympus 2.5x NFK photoeyepiece and a Canon EOS R7 camera (auto white balance). Single images, no stacking, and full frames are shown without cropping.

Imaging of different slides done as follows:

Fluorescence: 365nm LED torch, with ZWB2 filter on the front (probably 2mm). 3mm thick GG420 filter on top of the photoeyepiece.

Bright field: White LED light. 3mm thick GG420 filter on top of the photoeyepiece.

Cross polarized: White LED light. Linear polarizer on the field lens. Moxtek linear polarizer on top of the photoeyepiece. Polarizers rotated to extinction.

1st sample. A thin section (about 30µm) mounted in Petropoxy 154 resin and with a coverslip. The rock is at the bottom of the image, then a thin layer of lichen, and at the top of the image the mount. Shown as fluorescence, bright field, and cross polarized images.

Fluorescence image
Bright field
Cross polarized

What’s going on with these images? In the bright field image, the thin rock sample looks fairly transparent as does the mount. The lichen looks to be quite dark in the bright field image, with a sort of ‘powdery’ appearance. The orange colour from the lichen seems to have dispersed into the mount a bit. This is also obvious in the fluorescence image where now the lichen itself looks to be quite transparent but there is a strong orange fluorescence surrounding it. In the cross polarized image the lichen is no longer really obvious (although there is a slight orange/yellow look to parts of the surface of the rock), but the different crystals in the rock are now really visible.

Given the bleed of the orange from the lichen in the Petropoxy 154 mount, Dr Beard suggested he could try using a different mount for some other slides, and so that is what he did.

Next, a thicker sample (about 60µm) with no coverslip.

Fluorescence
Bright field
Cross polarized

Again the rock is towards the bottom of the image. The top is now open space. This sample looks different to the first as it is thicker and has no coverslip. It is therefore more 3D in appearance. The lichen now shows as a general orange glow at the surface of the rock in the openings in between the individual grains. Nice colours in the cross polarized image but as these are thicker and not well defined slices, it doesn’t look the same as the thin section in the 1st set of images.

As a final set of images, these were also done with the newer mount, and as a thin section with a coverslip. This does not show the surface of the rock, but was an area of the matrix which had glowed yellow under 365nm light.

Fluorescence
Bright field
Cross polarized

There is a strong yellow fluorescence which looks to be coming from whatever is in between some of the individual grains which make up the rock. This was quite heterogeneous across the sample, and this was an area where the yellow fluorescence was particularly strong. The bright field image doesn’t really show us a lot, although there is a slight colouration on the areas which fluoresce. The cross polarized image shows the typical appearance of a thin section again. The areas which fluoresce yellow look different – not black/grey/white but more rainbow coloured. Presumably these are a different mineral to the grains. It reminds me a bit of the Yooperlite mineral I imaged here. I used fused silica for these slides as glass will block short wavelength UV. It is a bit overkill for 365nm light, but does allow me to try shorter wavelengths in the future if I want to.

Overall I am really happy with the samples prepared by Dr Beard at Geology Hub, and they enabled me to have a look at the Tasmanian rock sample under the microscope. Changing the mode of imaging (fluorescence, bright field and cross polarized) had a huge impact on the appearance of the sample. As always thanks for reading, and if you’d like to know more about my work, I can be reached here.