Cleanliness of Zeiss 1.5H cover slips

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viktor j nilsson
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Cleanliness of Zeiss 1.5H cover slips

#1 Post by viktor j nilsson » Wed Feb 10, 2021 12:55 pm

I'm interested in hearing about people's experiences with Zeiss 1.5H high precision cover slips. I stumbled upon a great deal for a large amount of these, and picked up all that the seller had. They all came came in original zip lock bags.

I've only tried a handful yet, but I was a little surprised that they were quite dusty. Thickness has been spot on with the ones I've measured, but they are much less clean than I had expected from such premium cover slips. They do seem to clean up well with dish washing detergent, however.

Is this consistent with other people's experiences?
Last edited by viktor j nilsson on Thu Feb 11, 2021 5:44 am, edited 1 time in total.

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Re: Cleanliness of Zeiss 1.5H cover slips

#2 Post by quantum » Wed Feb 10, 2021 4:39 pm

My only experience is with Amscope coverslips and similar, purchased new on eBay. If I look carefully there is fine "dust" on the coverslips. I have always assumed that this was part of the manufacturing and packing process, and maybe even is necessary to let them slide one atop the other, instead of sticking or galling. (This is speculation though.)

Almost always, it is totally okay and unless I try to focus on the dust it is not a problem. Sometimes, if it really matters and I want everything in the optical path to be super duper clean, I clean the cover slip too.

Others might know more about this than I do.

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Re: Cleanliness of Zeiss 1.5H cover slips

#3 Post by viktor j nilsson » Wed Feb 10, 2021 5:22 pm

Yes, I definitely expect cheap cover slips to be dirty. But the 1.5H high precision cover slips are many times more expensive. The price tag comes from their much tighter tolerances in thickness, but I wasn't sure if they would also be cleaner than other cover slips. But based on input on another thread I started over on photomacrography.net, it seems like this is normal for all coverslip/slide brands regardless of their price tag - some grease and dust on the glass inevitably results from the glass cutting process.

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Re: Cleanliness of Zeiss 1.5H cover slips

#4 Post by MicroBob » Wed Feb 10, 2021 5:31 pm

Hi Viktor,
I also bought Zeiss cover slips from an ebay seller. He said they were included with Zeiss Objectives and not needed wich I don't doubt. They have a very even thickness of slightly over 0,17mm, ca. 0,175, within tolerance but probably near the upper limit. A micrometer is not really specified for measuring beyond the ,xx so this is just a tendency.
They are clean enough for most purposes but not perfectly clean. At least part of the dust seems to be glass as it makes crunching noises when flattening it with the micrometer anvils. There may be even cleaner cover slips available, but wouldn't they need a different package too? The dust wides away with a dry paper tissue, so it is an easy last step.

Perhaps with cover slips it is like with objectives: There are plan obectives and apochromatic objectives but neither has the advantage of the other. So we should look for precision/clean cover slips an prepare out wallets for them...

If possible I make my preparations on the cover slip so the specimen is closest to the optimum distance for the objective. Here a lillte dust can be a disadvantage, especially in dark field microscopy.

Bob

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Re: Cleanliness of Zeiss 1.5H cover slips

#5 Post by quantum » Wed Feb 10, 2021 5:34 pm

My suggestion was that what you are calling "dirty" might be on purpose. Talc, for example. Extremely flat glass surfaces do tend to stick together.

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Re: Cleanliness of Zeiss 1.5H cover slips

#6 Post by zzffnn » Wed Feb 10, 2021 5:41 pm

I have those Zeiss; they have fine particles on them. Yes, likely talc, on purpose. They wipe off with cotton cloth easily.

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Re: Cleanliness of Zeiss 1.5H cover slips

#7 Post by viktor j nilsson » Wed Feb 10, 2021 5:42 pm

MicroBob wrote:
Wed Feb 10, 2021 5:31 pm
Hi Viktor,
I also bought Zeiss cover slips from an ebay seller. He said they were included with Zeiss Objectives and not needed wich I don't doubt. They have a very even thickness of slightly over 0,17mm, ca. 0,175, within tolerance but probably near the upper limit. A micrometer is not really specified for measuring beyond the ,xx so this is just a tendency.
They are clean enough for most purposes but not perfectly clean. At least part of the dust seems to be glass as it makes crunching noises when flattening it with the micrometer anvils. There may be even cleaner cover slips available, but wouldn't they need a different package too? The dust wides away with a dry paper tissue, so it is an easy last step.

Perhaps with cover slips it is like with objectives: There are plan obectives and apochromatic objectives but neither has the advantage of the other. So we should look for precision/clean cover slips an prepare out wallets for them...

If possible I make my preparations on the cover slip so the specimen is closest to the optimum distance for the objective. Here a lillte dust can be a disadvantage, especially in dark field microscopy.

Bob
Might have been the same seller? He was located in Germany. I bought a couple of packages from him on eBay and bought the rest of his supply outside of eBay. I got the impression he was an honest guy.

I haven't tested the crunchiness of the dust, but it make sense that it's glass dust from the cutting process. I will try to find a cleaning process that strikes a reasonable balance between cleanliness, safety and my own restlessness :D

I've read that even the "pre-cleaned" cover slips aren't really clean enough for really good darkfield. And demanding users (like researchers with super resolution microscopes) always clean their cover slips regardless of brand. So I don't think there are any high precision/ultra clean cover slips you can buy - regardless of how much money you are willing to spend!

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Re: Cleanliness of Zeiss 1.5H cover slips

#8 Post by viktor j nilsson » Wed Feb 10, 2021 5:47 pm

quantum wrote:
Wed Feb 10, 2021 5:34 pm
My suggestion was that what you are calling "dirty" might be on purpose. Talc, for example. Extremely flat glass surfaces do tend to stick together.
zzffnn wrote:
Wed Feb 10, 2021 5:41 pm
I have those Zeiss; they have fine particles on them. Yes, likely talc, on purpose. They wipe off with cotton cloth easily.
Ah, sorry I somehow missed this second part of your argument, quantum. If demanding users always clean their slides anyway, it does make sense to cover them with something like that on purpose to protect the surface and allow them to separate more easily. Thanks guys, I hadn't thought of that!

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Re: Cleanliness of Zeiss 1.5H cover slips

#9 Post by viktor j nilsson » Thu Feb 11, 2021 2:55 pm

First, I found an earlier very good thread on this topic that gave me a lot of ideas. I'll add it here for future reference:
viewtopic.php?t=2107

Second, I've spent a good couple of hours testing different ways of cleaning the Zeiss cover glass. Turns out cleaning them is easy. But drying is hard!

To clean, I tried much of what I had on hand in reasonable quantities: white vinegar (24% acetic acid), window cleaner with ammonium, isopropanol, dish washing liquid. Tried soaking, rubbing, rinsing and sweeping the glass through the liquid with most of them.

The method I preferred was to simply dunk the cover glass in lukewarm water with dish washing liquid (a brand called Yes here in Sweden) and gently rubbing them between my fingers. None of the other methods did any harm, but I didn't feel that they made the glass any cleaner than dish washing liquid alone.

Then came the tricky part: drying.

I tried a bunch of different methods: canned air, camera lens puffer, hair dryer, leaving them to dry, kimwipes, microfiber rags, microfiber cloth for cleaning eye glasses, old cotton t-shirts, linen tea towels.

None of the mechanical drying methods were good enough in my opinion. The linen tea towel worked the best, especially when followed by a few puffs of air. The tightly woven microfiber cloth for glasses was the second best. But even if I used the puffer or canned air afterwards, any method that involved rubbing the cover glass between any kind of tissue left too much fibers and dust for my liking.

Air drying after rinsing with tap water left significant marks where the last water drops had evaporated (hard water here).

The hair dryer was too slow, and also left marks.

The canned air method was quite promising, as it quickly pushed away the water to the edges, leaving a very clean area in the middle. I'm not too keen on using up a lot of cans of air, though, for environmental reasons. But it made me realize how good it is to get the liquid away from the central area as quick as possible.

This led me to the method that I liked the best. After cleaning with dish washing liquid, I held the cover glass vertically (using fine tweezers) under the tap and flushed it with a rapid stream of warm water. Then, if I passed the cover glass through the water at a very specific speed, I was able to get the water to recede to one side very evenly, leaving the vast majority of the cover glass area very clean indeed. The only area where some water drops remained was along the edges and around the forceps. After this, i gently laid the cover glass on a piece of kimwipe to absorb the last remaining drops, being careful not to move it around so as to not release any fibers, flipping it over to try dry the other side, again without moving it around.

This produced a cover glass that I was quite happy about: none of the earlier grease or dust remained, and almost no dust from the drying process had been added. Any drying marks from the water were only found around the edges of the cover slip, which I'm okay with.

I'm sure that rinsing with alcohol might be even better than tap water, but for environmental and economical reasons I prefer to use such things more sparingly.

Any other suggestions are welcome!

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Re: Cleanliness of Zeiss 1.5H cover slips

#10 Post by MicroBob » Thu Feb 11, 2021 3:48 pm

Hi Viktor,
for cleaning lenses I use "Wundbenzin", medical spirit, which is similar to lighter fluid but cleaner.
For fairly dirty new cover slips I took a 53ml marmelade glass, threw them all in and filled op with isopropanol. If need one i fish it out with forceps and clean it with papaer tissue and blowing. For the Zeiss cover slips I would be fine with just dry cleaning and blowing off the last specs of dust.

Bob

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Re: Cleanliness of Zeiss 1.5H cover slips

#11 Post by viktor j nilsson » Thu Feb 11, 2021 4:09 pm

MicroBob wrote:
Thu Feb 11, 2021 3:48 pm
Hi Viktor,
for cleaning lenses I use "Wundbenzin", medical spirit, which is similar to lighter fluid but cleaner.
For fairly dirty new cover slips I took a 53ml marmelade glass, threw them all in and filled op with isopropanol. If need one i fish it out with forceps and clean it with papaer tissue and blowing. For the Zeiss cover slips I would be fine with just dry cleaning and blowing off the last specs of dust.

Bob
Using the paper tissue and blower method, do you get them clean enough for brightfield, or do you get them really really clean? As in clean enough for high NA darkfield? I've adapter my Heine for my Vanox and started using it for high NA darkfield, so I'm hoping to get the cover slips really really clean.

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Re: Cleanliness of Zeiss 1.5H cover slips

#12 Post by MicroBob » Thu Feb 11, 2021 4:24 pm

Good enough for my needs and available time. Probably not good enough for yours though.

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Re: Cleanliness of Zeiss 1.5H cover slips

#13 Post by viktor j nilsson » Thu Feb 11, 2021 4:40 pm

MicroBob wrote:
Thu Feb 11, 2021 4:24 pm
Good enough for my needs and available time. Probably not good enough for yours though.
Honestly, I think they would be clean enough for me as well. I've always used cover slips straight out of the box and haven't really been too bothered. I've just gotten curious to see how big of a difference it makes, and what it takes to get them really clean.

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Re: Cleanliness of Zeiss 1.5H cover slips

#14 Post by MicroBob » Thu Feb 11, 2021 8:40 pm

I once had a closer look at a lot of slides and cover slips of very different origin and age. I found most cover slips to be in usable condition but of cause of different states of cleanliness. With the slides it is very different: Here sometimes two year old packages already had a decayed surface that didn't clean up when cleaning. The difference between cover slips and slides is the glass type: Cover slips are usually from borosilicat glass, slides from soda lime glass, which is hygroscopic and parts can be dissolved from the surface.
Apparently the decaying takes place in the packages, not so much when slides are stored separately in slide boxes. Probably moisture collects between the closely stacked slides and doesn more harm than on the free standing slide.

So when optimizing slide making for dark field I would also look closely at the slides.

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Re: Cleanliness of Zeiss 1.5H cover slips

#15 Post by viktor j nilsson » Thu Feb 11, 2021 8:48 pm

MicroBob wrote:
Thu Feb 11, 2021 8:40 pm
I once had a closer look at a lot of slides and cover slips of very different origin and age. I found most cover slips to be in usable condition but of cause of different states of cleanliness. With the slides it is very different: Here sometimes two year old packages already had a decayed surface that didn't clean up when cleaning. The difference between cover slips and slides is the glass type: Cover slips are usually from borosilicat glass, slides from soda lime glass, which is hygroscopic and parts can be dissolved from the surface.
Apparently the decaying takes place in the packages, not so much when slides are stored separately in slide boxes. Probably moisture collects between the closely stacked slides and doesn more harm than on the free standing slide.

So when optimizing slide making for dark field I would also look closely at the slides.
This is very true!
In fact, part of the reason for bringing out all the different cleaning agents today was to see if there was anything I could do to save a big box of slides that came with my 1970s olympus Vanox. They are all really hazy and very firmly attached to each other in their packages. White vinegar cleared the haze very well and they looked quite nice to the naked eye. However, nothing was able to fix the biggest problem: the surface of each slide is sprinkled with tiny little pits. It's like looking at a starry night sky when viewed at 40x in darkfield. I can probably still use them for non-critical microscopy (like checking mushroom spores), but they will never work properly for darkfield, that's for sure.

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Re: Cleanliness of Zeiss 1.5H cover slips

#16 Post by Wes » Thu Feb 11, 2021 8:57 pm

viktor j nilsson wrote:
Wed Feb 10, 2021 12:55 pm
Is this consistent with other people's experiences?
Its consistent with my experience. I've tried 1.5H coverslips from another manufacturer and they seemed cleaner but still warrant a wipe. At some point I tried various cleaning methods and by far the best method is cleaning with piranha solution. But it goes without saying I wouldn't not recommend this method to the casual hobbyist as it is extremely dangerous. First I do a detergent wash and then the piranha, ridiculously clean slides result but cleanliness doesn't last as they adsorb environmental contaminants over time. Usually only required for chemically modifying the glass the surface (I only tried for diatom arrangements in Pleurax using a polyacrylamide based adhesive).
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Re: Cleanliness of Zeiss 1.5H cover slips

#17 Post by viktor j nilsson » Thu Feb 11, 2021 9:21 pm

Wes wrote:
Thu Feb 11, 2021 8:57 pm
viktor j nilsson wrote:
Wed Feb 10, 2021 12:55 pm
Is this consistent with other people's experiences?
Its consistent with my experience. I've tried 1.5H coverslips from another manufacturer and they seemed cleaner but still warrant a wipe. At some point I tried various cleaning methods and by far the best method is cleaning with piranha solution. But it goes without saying I wouldn't not recommend this method to the casual hobbyist as it is extremely dangerous. First I do a detergent wash and then the piranha, ridiculously clean slides result but cleanliness doesn't last as they adsorb environmental contaminants over time. Usually only required for chemically modifying the glass the surface (I only tried for diatom arrangements in Pleurax using a polyacrylamide based adhesive).
Thanks for confirming that it's consistent with your experience.

I read up on piranha solution. Yikes! I do not want to deal with that in my home office, which is adjacent to the kids' room... :o

However, this led me to some discussions about safer alternatives, and it seems like a lot of people clean glassware using a mixture of KOH and Ethanol or Isopropanol (sometimes NaOH instead of KOH). I have KOH tablets at hand (I use it to clear fly genitalia), so I might try that with cover slips. But that's for another day.

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Re: Cleanliness of Zeiss 1.5H cover slips

#18 Post by viktor j nilsson » Thu Feb 11, 2021 9:22 pm

Btw, how do you dry the cover glass after the piranha bath?

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Re: Cleanliness of Zeiss 1.5H cover slips

#19 Post by Wes » Thu Feb 11, 2021 9:28 pm

viktor j nilsson wrote:
Thu Feb 11, 2021 9:21 pm
Wes wrote:
Thu Feb 11, 2021 8:57 pm
viktor j nilsson wrote:
Wed Feb 10, 2021 12:55 pm
Is this consistent with other people's experiences?
Its consistent with my experience. I've tried 1.5H coverslips from another manufacturer and they seemed cleaner but still warrant a wipe. At some point I tried various cleaning methods and by far the best method is cleaning with piranha solution. But it goes without saying I wouldn't not recommend this method to the casual hobbyist as it is extremely dangerous. First I do a detergent wash and then the piranha, ridiculously clean slides result but cleanliness doesn't last as they adsorb environmental contaminants over time. Usually only required for chemically modifying the glass the surface (I only tried for diatom arrangements in Pleurax using a polyacrylamide based adhesive).
Thanks for confirming that it's consistent with your experience.

I read up on piranha solution. Yikes! I do not want to deal with that in my home office, which is adjacent to the kids' room... :o

However, this led me to some discussions about safer alternatives, and it seems like a lot of people clean glassware using a mixture of KOH and Ethanol or Isopropanol (sometimes NaOH instead of KOH). I have KOH tablets at hand (I use it to clear fly genitalia), so I might try that with cover slips. But that's for another day.
NaOH is what I initially used when attempting to clean slips. However, it roughened the glass surface, not what I was looking for. Strong alkali bases etch glass but I might have kept it for too long, but I got different results with different coverslips so it might work well for you.
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Re: Cleanliness of Zeiss 1.5H cover slips

#20 Post by Wes » Thu Feb 11, 2021 9:29 pm

viktor j nilsson wrote:
Thu Feb 11, 2021 9:22 pm
Btw, how do you dry the cover glass after the piranha bath?
Multiple washes with deionized water, then submerge the coverlips under ethanol. Whenever I need a coverslip I use tweezers to grab one and let the ethanol evapore on its own, it doesn't leave traces if its sufficiently clean.
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Re: Cleanliness of Zeiss 1.5H cover slips

#21 Post by viktor j nilsson » Thu Feb 11, 2021 9:39 pm

Wes wrote:
Thu Feb 11, 2021 9:29 pm
viktor j nilsson wrote:
Thu Feb 11, 2021 9:22 pm
Btw, how do you dry the cover glass after the piranha bath?
Multiple washes with deionized water, then submerge the coverlips under ethanol. Whenever I need a coverslip I use tweezers to grab one and let the ethanol evapore on its own, it doesn't leave traces if its sufficiently clean.
I see, that sounds convenient. Thanks, I shall try it.

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Re: Cleanliness of Zeiss 1.5H cover slips

#22 Post by Hobbyst46 » Thu Feb 11, 2021 10:09 pm

I clean by boiling the coverslips (not Zeiss, much cheaper stuff) in tap water for 15 minutes (same as hard boiling an egg). Then rinse with distilled water and lay on a KimWipe to dry. Then store in a closed Lock-Lock box.

Yet the appearance of tiny dust and fibers from air, during slide preparation, is unavoidable... so darkfield does reveal the specks.

Moreover, diatom adhesive catches dust and other tiny unwanted things, while it dries. Although, prior to spreading the adhesive on a cleaned cover-slip, I filter it with a 0.45 um filter on top of a disposable syringe.

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