I'll demonstrate one way to make thin sections. It's easier than you might think! Etsy: donohuelabs.etsy.com/ Help support the channel: ko-fi.com/donohuelabs
Some tips: The first side (before gluing to the slide) needs to be polished down as much as you can as well (preferrably with alumina or diamond paste to 0.25 um abrasive size). The sample needs to be thoroughly cleaned between steps (e.g with ultrasonic cleaner) to remove abrasive material. Instead of holding the sample in one position, it is better to do figure of 8s to create an uniform thickness. Gluing pieces of glass at the corners can also help with that. Although i agree that it can be done using a rock saw and sandpaper, thin-section preparation requires a lot of practice to achieve the technique to make good thin sections.
When using a grinding disk, you run the risk of grinding down the center of the disk, puttingva grive inbyour disk, leaving raised dimond edges along the margins over time.
Thanks Patrick. My uncle used to work in the Geology dept of Uni of New Brunswick and I wondered what it might involve. Your results blew me away. Thanks again
Perhaps the grinding could be made a little easier by putting a dop stick on the back of the slide so when putting the down pressure on the slide you can lift in up with ease and all the pressure is in the correct place.
Few comments. Frosting the slide is only good if your adheaive has a similar RI to the glass. It is good to do to flatten the glass. Agate is banded or varigated chalcedony. Your sample was not agate. Also, if you are sectioning carbonates etc, it is handy to glue a couple of quartz grains on each side beside your sample to use as a reference.
That was really interesting. I thought there is no way this is going to work with these but pieces of rock! But with a lot of determination and a lap, I'll be damned if you didn't do it! That's pretty cool! And although most of us don't have a compound microscope, you got some pretty good pictures! Awesome video!
Great video! The steps were very informative and definitely gives a sense of accessibility for anyone to try. Of course it's super cool to see the thin sections magnified with the microscope, but even the thins close up at lower magnification (loupe) were really interesting to see that way. Hopefully folks will be tempted to view some of their mineral treasures in a closer way from this. Thanks for sharing your experience, cheers!
You can examine the thin section between two sheets of "polaroid" (other trade marks are available!) to bring out the interference colours. Then a regular hand lens or microscope will allow you to see some of the detail. But interpretative work (mineral grain compositions within series, for example) typically need a rotating stage too. Hmmm, I've got a rotating photographic filter holder (for "star burst" effects, etc) which might help. But then, I've also got a petrographic microscope form when the college shrank it's geology department size.
Thank you for the demonstration. I enjoyed it very much. An idea for future attempts at making a thin section with parallel sides and to facilitate accurate thickness measurement during manufacturing. Float glass is extremely flat. I suspect that the microscope slides are also very flat. lets take advantage of that to be our guide to machining a thin section to be nearly perfectly parallel and meet dimensional specifications. Grind, lap and polish a flat surface on the artifact, to a surface RMS that is required for microscopic use. Method to adhere a specimen with superglue to a glass slide that has groves to accept the adhesive. Etch many parallel groves into the glass slide, lengthwise. Make the groves deep enough to accept a thin film of the adhesive, experiment until you find a good ratio of depth to width. The depth and width of the groves depends on the viscosity of the adhesive. Our goal is to wick the adhesive under the specimen and to avoid getting 'any' adhesive between the glass slide and the specimen. Before placing the specimen onto the glass slide, load the etched groves with adhesive. Add adhesive until the meniscus reaches up to the surface and not above the glass. We want to avoid any glue on the surface of the glass. Use a split toothpick to encourage the adhesive into the grove. It's best to do this in a low humidity environment, as superglue kicks off with moisture. To get the glue onto the specimen. Drop the specimen onto the glass slide, don't move it. At the perimeter of the specimen add more adhesive into the groves in the glass. The adhesive will wick into and under the specimen, providing that the grove width and depth are sized properly. To speed up the curing and to encourage curing of the adhesive under the specimen. Mist a small amount of distilled water at the perimeter of the specimen onto of the groves. Follow the manufacturers cure time before lapping. There are solvents that will break the bonds of superglue. So if you want a clearer picture of the thin section, consider removing the specimen from the superstructure. And apply it to a new glass slide. I hope you can make sense of what I have described. Thanks again for sharing your experience with us! You have given me ideas for making beautiful 'things'.
You make some interesting points. I hesitate to carve too much into the slides because they are thin, and also a big groove would cause aberration in transmitted light. But I certainly didn't need as much CA glue as I used, and I kind of like the idea of letting the glue seep in under the edge to minimize the glue thickness.
@@DonohueLabs If you used 1/8" to 1/4" thick float glass you will have plenty of thickness to work with. You will be hard pressed to find anything flatter. Float glass will also not be prone to flexing as much as the glass slide. The thickness will also make it easier for you to grip. Ideally you would finish one side of the specimen to a high polish. Separate it from the glass while it's still has it's strength/integrity and glue the finished side down. When the desired thickness is achieved, carefully remove it and place it onto a clean glass slide. Mineral oil could be used to hold it in place. One grove on two sides of the specimen may be all that's needed to retain the specimen. Maybe baking soda could be added for additional strength? The only iffy aspect is removing it and handling it after it's finished. There are also different viscosities of superglue. Use the type that flows like water, the gels are not suited for this. Tks!
@@DonohueLabs Glue thickness isn't a problem. It's isotropic and (should be) colourless. (That's why "resin impregnation" is a step taken *before* gluing the proto-slide to it's microscope slide. The glue that penetrates into cracks, grain boundaries etc provides a reference refractive index for the "Becke Line Test", where on up-focussing, the refracted bright line moves into the higher RI medium. (Hence the importance of the RI of the glue.) After thinning the slide to 30µm, you apply more glue to the surface of the slide and glue a cover slip onto it to protect the side and allow Becke tests for top-surface fractures. (For polished (µ-probe) samples, the top surface need to be open to air/ vacuum.) Trying to "seep" the glue as you describe is likely to leave parts of the slide un-attached to the glass, which would fragment during the thinning stage, meaning a complete re-start. You don't want to do that.
@@pigeonbloodruby5330That thick a float glass would introduce colour banding under cross polarised light (which is why you cut thin sections) because of residual strain in the glass. That would complicate interpretation of mineral identities, textures and compositions -some of the tests that need a £1500 microscope need careful optical testing ; the alternative is a £200000 microprobe, and a vibration-proofed lab to house it. Microscope slides are float glass anyway. Just about a half-mm thick. You could fill your windows with it, and watch it break in the wind. "The only iffy aspect is removing it and handling it after it's finished." The 30µm thick rock sample? It'd crumble to powder. Even good commercial slide preparation labs lose several percent of their slide to this (and have to re-start the process). at 30µm thick by 20mm wide it has an aspect ratio 1:600 - which would be like a wall tile about 6m wide - very very fragile. "There are also different viscosities of superglue. Use the type that flows like water, the gels are not suited for this." Viscosity is pretty unimportant (within reason) - the refractive index needs to be 1.54 to 1.56 (to match "Canada Balsam". Otherwise the minerals just look peculiar, greatly increasing the time and cost of interpretation.
The slide-frosting step is unnecessary, if you clean and dry your slide (and rock) before gluing it. I know you're using existing tools, but putting a sheet of glass onto the lap and using loose grits would probably work quicker and better. Gluing the specimens down would work better by putting one bead of adhesive along the specimen edge, then tilting the specimen onto the slide. A little jiggle to move bubbles off to the side. Do you know the "sand grain" technique for getting thickness references into your slide? At standard thickness (30µm), between crossed polars ("polaroid" etc), the brightest colours you'll get from a sand grain will be first-order white. With sheet polaroid and a hand lens, you should be able to check this. "Compound" microscopes in general can't do reflected light microscopy - for that you need a "reflected light microscope". "compound" means several lenses in the "objective" assembly, and more lenses up the tube constituting the "eyepiece". Petrographic microscopes have tools ("polars", other lenses) between the objective and the eyepiece.
Pretty much! It just has to hold together during grinding, and can't be water soluble. You CAN do water soluble materials, but you have to use other liquids like acetone or methanol. That's what they use for some meteorites.
@@DonohueLabs Preparing thin sections of evaporite minerals (i.e. water soluble) is a recognised field technique, using as you say, non-water solvents. But it's extremely time consuming, and generally unnecessary to know *at the field site*. You do your mapping, collect your samples, and do that sort of detail back at the office outside the field season.
Some tips:
The first side (before gluing to the slide) needs to be polished down as much as you can as well (preferrably with alumina or diamond paste to 0.25 um abrasive size).
The sample needs to be thoroughly cleaned between steps (e.g with ultrasonic cleaner) to remove abrasive material.
Instead of holding the sample in one position, it is better to do figure of 8s to create an uniform thickness. Gluing pieces of glass at the corners can also help with that.
Although i agree that it can be done using a rock saw and sandpaper, thin-section preparation requires a lot of practice to achieve the technique to make good thin sections.
When using a grinding disk, you run the risk of grinding down the center of the disk, puttingva grive inbyour disk, leaving raised dimond edges along the margins over time.
Thanks Patrick. My uncle used to work in the Geology dept of Uni of New Brunswick and I wondered what it might involve. Your results blew me away. Thanks again
Very cool! This is just one low tech way to do it, I'm sure he had much better tools at hand to do this stuff (lucky him!)
Perhaps the grinding could be made a little easier by putting a dop stick on the back of the slide so when putting the down pressure on the slide you can lift in up with ease and all the pressure is in the correct place.
Few comments. Frosting the slide is only good if your adheaive has a similar RI to the glass. It is good to do to flatten the glass. Agate is banded or varigated chalcedony. Your sample was not agate.
Also, if you are sectioning carbonates etc, it is handy to glue a couple of quartz grains on each side beside your sample to use as a reference.
That was really interesting. I thought there is no way this is going to work with these but pieces of rock! But with a lot of determination and a lap, I'll be damned if you didn't do it! That's pretty cool! And although most of us don't have a compound microscope, you got some pretty good pictures! Awesome video!
Dang! That was awesome. Nice job. Looking forward to seeing George Rock Nerd's vid.
Great video! The steps were very informative and definitely gives a sense of accessibility for anyone to try. Of course it's super cool to see the thin sections magnified with the microscope, but even the thins close up at lower magnification (loupe) were really interesting to see that way. Hopefully folks will be tempted to view some of their mineral treasures in a closer way from this. Thanks for sharing your experience, cheers!
And I'm looking forward to your thin section video!
You can examine the thin section between two sheets of "polaroid" (other trade marks are available!) to bring out the interference colours. Then a regular hand lens or microscope will allow you to see some of the detail. But interpretative work (mineral grain compositions within series, for example) typically need a rotating stage too.
Hmmm, I've got a rotating photographic filter holder (for "star burst" effects, etc) which might help. But then, I've also got a petrographic microscope form when the college shrank it's geology department size.
Thank you for the demonstration. I enjoyed it very much.
An idea for future attempts at making a thin section with parallel sides and to facilitate accurate thickness measurement during manufacturing.
Float glass is extremely flat. I suspect that the microscope slides are also very flat. lets take advantage of that to be our guide to machining a thin section to be nearly perfectly parallel and meet dimensional specifications.
Grind, lap and polish a flat surface on the artifact, to a surface RMS that is required for microscopic use.
Method to adhere a specimen with superglue to a glass slide that has groves to accept the adhesive.
Etch many parallel groves into the glass slide, lengthwise. Make the groves deep enough to accept a thin film of the adhesive, experiment until you find a good ratio of depth to width. The depth and width of the groves depends on the viscosity of the adhesive. Our goal is to wick the adhesive under the specimen and to avoid getting 'any' adhesive between the glass slide and the specimen.
Before placing the specimen onto the glass slide, load the etched groves with adhesive. Add adhesive until the meniscus reaches up to the surface and not above the glass. We want to avoid any glue on the surface of the glass. Use a split toothpick to encourage the adhesive into the grove. It's best to do this in a low humidity environment, as superglue kicks off with moisture.
To get the glue onto the specimen. Drop the specimen onto the glass slide, don't move it. At the perimeter of the specimen add more adhesive into the groves in the glass. The adhesive will wick into and under the specimen, providing that the grove width and depth are sized properly.
To speed up the curing and to encourage curing of the adhesive under the specimen. Mist a small amount of distilled water at the perimeter of the specimen onto of the groves. Follow the manufacturers cure time before lapping.
There are solvents that will break the bonds of superglue. So if you want a clearer picture of the thin section, consider removing the specimen from the superstructure. And apply it to a new glass slide.
I hope you can make sense of what I have described.
Thanks again for sharing your experience with us! You have given me ideas for making beautiful 'things'.
You make some interesting points. I hesitate to carve too much into the slides because they are thin, and also a big groove would cause aberration in transmitted light. But I certainly didn't need as much CA glue as I used, and I kind of like the idea of letting the glue seep in under the edge to minimize the glue thickness.
@@DonohueLabs If you used 1/8" to 1/4" thick float glass you will have plenty of thickness to work with. You will be hard pressed to find anything flatter. Float glass will also not be prone to flexing as much as the glass slide. The thickness will also make it easier for you to grip.
Ideally you would finish one side of the specimen to a high polish. Separate it from the glass while it's still has it's strength/integrity and glue the finished side down. When the desired thickness is achieved, carefully remove it and place it onto a clean glass slide. Mineral oil could be used to hold it in place.
One grove on two sides of the specimen may be all that's needed to retain the specimen. Maybe baking soda could be added for additional strength?
The only iffy aspect is removing it and handling it after it's finished.
There are also different viscosities of superglue. Use the type that flows like water, the gels are not suited for this.
Tks!
@@DonohueLabs Glue thickness isn't a problem. It's isotropic and (should be) colourless. (That's why "resin impregnation" is a step taken *before* gluing the proto-slide to it's microscope slide.
The glue that penetrates into cracks, grain boundaries etc provides a reference refractive index for the "Becke Line Test", where on up-focussing, the refracted bright line moves into the higher RI medium. (Hence the importance of the RI of the glue.)
After thinning the slide to 30µm, you apply more glue to the surface of the slide and glue a cover slip onto it to protect the side and allow Becke tests for top-surface fractures.
(For polished (µ-probe) samples, the top surface need to be open to air/ vacuum.)
Trying to "seep" the glue as you describe is likely to leave parts of the slide un-attached to the glass, which would fragment during the thinning stage, meaning a complete re-start. You don't want to do that.
@@pigeonbloodruby5330That thick a float glass would introduce colour banding under cross polarised light (which is why you cut thin sections) because of residual strain in the glass. That would complicate interpretation of mineral identities, textures and compositions -some of the tests that need a £1500 microscope need careful optical testing ; the alternative is a £200000 microprobe, and a vibration-proofed lab to house it.
Microscope slides are float glass anyway. Just about a half-mm thick. You could fill your windows with it, and watch it break in the wind.
"The only iffy aspect is removing it and handling it after it's finished." The 30µm thick rock sample? It'd crumble to powder. Even good commercial slide preparation labs lose several percent of their slide to this (and have to re-start the process). at 30µm thick by 20mm wide it has an aspect ratio 1:600 - which would be like a wall tile about 6m wide - very very fragile.
"There are also different viscosities of superglue. Use the type that flows like water, the gels are not suited for this." Viscosity is pretty unimportant (within reason) - the refractive index needs to be 1.54 to 1.56 (to match "Canada Balsam". Otherwise the minerals just look peculiar, greatly increasing the time and cost of interpretation.
The slide-frosting step is unnecessary, if you clean and dry your slide (and rock) before gluing it.
I know you're using existing tools, but putting a sheet of glass onto the lap and using loose grits would probably work quicker and better.
Gluing the specimens down would work better by putting one bead of adhesive along the specimen edge, then tilting the specimen onto the slide. A little jiggle to move bubbles off to the side.
Do you know the "sand grain" technique for getting thickness references into your slide? At standard thickness (30µm), between crossed polars ("polaroid" etc), the brightest colours you'll get from a sand grain will be first-order white. With sheet polaroid and a hand lens, you should be able to check this.
"Compound" microscopes in general can't do reflected light microscopy - for that you need a "reflected light microscope". "compound" means several lenses in the "objective" assembly, and more lenses up the tube constituting the "eyepiece". Petrographic microscopes have tools ("polars", other lenses) between the objective and the eyepiece.
Can you do this with any stone?
Pretty much! It just has to hold together during grinding, and can't be water soluble. You CAN do water soluble materials, but you have to use other liquids like acetone or methanol. That's what they use for some meteorites.
@@DonohueLabs Preparing thin sections of evaporite minerals (i.e. water soluble) is a recognised field technique, using as you say, non-water solvents. But it's extremely time consuming, and generally unnecessary to know *at the field site*. You do your mapping, collect your samples, and do that sort of detail back at the office outside the field season.