Too often after several minutes of browsing a pond sample slide I find something really interesting and make adjustments for a perfect photo - and a "wave" of water caused by evaporation comes and moves everything. How to deal with evaporation? I've seen something about using petroleum jelly, is it effective and practical? I don't really understand how to apply it.
Related question: do you press a bit on a cover slip after mounting? I do, otherwise it's a bit too thick even with a very small drop. On the other hand, some tiny amount of water escapes underneath the cover slip borders after pressing, is it excepted? Or should I use even smaller drop?
Dealing with evaporation
Re: Dealing with evaporation
Better to use a thick mount and low light/heat for scanning at 4x-10x objectives. Then very gently press cover slip, if you have to (or use a cotton swap to suck water away from cover slip edge, which will reduce mount thickness the same way as pressing). Lots of water and protists will be pushed out, if you press too hard and too early.
I prefer to add water, in amounts of around 3 microliter each time/spot, when I have to (with a research micro pipette). Petroleum jelly may not be easy to use.
I prefer to add water, in amounts of around 3 microliter each time/spot, when I have to (with a research micro pipette). Petroleum jelly may not be easy to use.
Re: Dealing with evaporation
Bonjour
La glycérine liquide fonctionne très bien pas évaporation.
En plus ça permet de garder la lame ainsi monté pendants plusieurs jours pour une nouvelle observation.
Cordialement seb
La glycérine liquide fonctionne très bien pas évaporation.
En plus ça permet de garder la lame ainsi monté pendants plusieurs jours pour une nouvelle observation.
Cordialement seb
Microscope Leitz Laborlux k
Boitier EOS 1200D + EOS 1100D
Boitier EOS 1200D + EOS 1100D
Re: Dealing with evaporation
(Note: I see Fan and vasselle have responded as I typed my reply... so I'm sorry for any duplication of thoughts. I suppose it doesn't hurt to hear it several different ways)
An ideal wet mount will have a very thin layer of water just "deep" enough to avoid crushing your subjects. Now for the ones we actually work with....
Various hard or dense pieces of the debris very commonly hold the coverslip up and keep it from settling flat and evenly as the water evaporates. The "wave" of water you are experiencing likely comes from the water evaporating to a point where air can rush in under the coverslip where it is slightly elevated. This disrupts everything in the water that remains.
A couple of things you can try. One is to avoid the particles that hold the coverslip slightly elevated. This is nearly impossible to do unless you can prepare your slide under a stereo microscope and are carefully selecting your subject matter with a fine pipette.
Another would be to avoid allowing the water to evaporate to the point where you have air incursion under the coverglass. Personally, rather than trying to seal a wet mount with petroleum jelly or similar substance I like to add tiny amount of water to the edge of the coverglass, where it is then "sucked in" by capillary action and after a few seconds becomes evenly distributed.
If you are working with wet mounts it is a good idea to have two things at hand. One would be a piece of lens cleaning paper or absorbent tissue, the other an fine pipette or eyedropper with a small container of water. If there is too much water in the mount you can hold the edge of the tissue up against the edge of the cover slip. This draws water out of the slip and allows you to "drop" the cover slip (at least up to the point where debris alone holds it up). If you find that evaporation is lowering the cover slip to the point where your subject is getting too flattened or crushed, or you can start to see the incursion of air around the edges of the coverslip, you can then add a small drop of water to the edge of the coverslip. As mentioned above, this is then "sucked in" by capillary action. In either scenario you need to allow a little time (maybe 15-30 seconds) for everything to stabilize before continuing with photography.
I typically avoid pushing a coverslip down (unless it it very clearly deeper than the thickest subject I might encounter) to avoid crushing any potential subjects.
An ideal wet mount will have a very thin layer of water just "deep" enough to avoid crushing your subjects. Now for the ones we actually work with....
Various hard or dense pieces of the debris very commonly hold the coverslip up and keep it from settling flat and evenly as the water evaporates. The "wave" of water you are experiencing likely comes from the water evaporating to a point where air can rush in under the coverslip where it is slightly elevated. This disrupts everything in the water that remains.
A couple of things you can try. One is to avoid the particles that hold the coverslip slightly elevated. This is nearly impossible to do unless you can prepare your slide under a stereo microscope and are carefully selecting your subject matter with a fine pipette.
Another would be to avoid allowing the water to evaporate to the point where you have air incursion under the coverglass. Personally, rather than trying to seal a wet mount with petroleum jelly or similar substance I like to add tiny amount of water to the edge of the coverglass, where it is then "sucked in" by capillary action and after a few seconds becomes evenly distributed.
If you are working with wet mounts it is a good idea to have two things at hand. One would be a piece of lens cleaning paper or absorbent tissue, the other an fine pipette or eyedropper with a small container of water. If there is too much water in the mount you can hold the edge of the tissue up against the edge of the cover slip. This draws water out of the slip and allows you to "drop" the cover slip (at least up to the point where debris alone holds it up). If you find that evaporation is lowering the cover slip to the point where your subject is getting too flattened or crushed, or you can start to see the incursion of air around the edges of the coverslip, you can then add a small drop of water to the edge of the coverslip. As mentioned above, this is then "sucked in" by capillary action. In either scenario you need to allow a little time (maybe 15-30 seconds) for everything to stabilize before continuing with photography.
I typically avoid pushing a coverslip down (unless it it very clearly deeper than the thickest subject I might encounter) to avoid crushing any potential subjects.
Re: Dealing with evaporation
Charles mentioned removing mineral particles, which is important too. You can do that by multiple rounds of filtration (with say a 500 micron kitchen screen, if your subject is smaller) and wash/precipitation by gravity (by avoiding the heaviest bottom layer of sand).
But mineral particles of around 30-100 microns are difficult to remove, whatever you do, if you are working with live bottom protists.
Lots of ciliates, for example, live at pond bottom close to sand. When you remove most sand particles, you would likely remove most ciliates too. There are exceptions, such as Paramecium Bursaria, which tend to float near water surface - with those, you can get a clean/thin mount without sand.
But mineral particles of around 30-100 microns are difficult to remove, whatever you do, if you are working with live bottom protists.
Lots of ciliates, for example, live at pond bottom close to sand. When you remove most sand particles, you would likely remove most ciliates too. There are exceptions, such as Paramecium Bursaria, which tend to float near water surface - with those, you can get a clean/thin mount without sand.
Re: Dealing with evaporation
Go to:
http://www.microscopy-uk.org.uk/mag/libindex.html
and search for valap
Lots of good info will pop up.
Have fun.
Brad
http://www.microscopy-uk.org.uk/mag/libindex.html
and search for valap
Lots of good info will pop up.
Have fun.
Brad
Re: Dealing with evaporation
For what it's worth old chap - I use the exact method outlined above by Charles - water along one edge of coverslip - tissue to 'suck the water across the specimen' against the opposite side of the coverslip - I use this technique for very sensitive application of stains and their differentiation - works very well indeed. 
John B
Re: Dealing with evaporation
Great, I'll try this method.mrsonchus wrote:For what it's worth old chap - I use the exact method outlined above by Charles - water along one edge of coverslip - tissue to 'suck the water across the specimen' against the opposite side of the coverslip - I use this technique for very sensitive application of stains and their differentiation - works very well indeed.