Birefringent graininess in cheap prepared slides

[hans]

As I mentioned in viewtopic.php?f=9&t=10021&start=150#p91060:

The quality of the prepared slides is not very good. I bought them used on eBay and there is no brand marking but they look very similar to what AmScope and others sell. Cover glass thickness seems ok but on many the sample is not very flat against the cover glass. There is also a weird transparent graininess to the mountant, almost like looking through mixing hot/cold water, which lights up as bright speckles when viewed with polarized light. Not sure what that is but is does not seem to affect the view at 10X much.

When I described it as looking like mixing hot/cold water I think that was a thicker sample or one with a higher density of the grains. Here is an example with lower density of the grains using brightfield, crossed polarizers, and crossed polarizers with full-wave plate. I assume this is not normal. Any speculation what this stuff is or what went wrong in the mounting process?

[hans]

Another example:

[mrsonchus]

Hi Hans, hmm the creature on the second slide, looks like internal contents to me but this isn't my area.

The Lily anther with pollen-grains, which appears to be stained with a haematoxylin with the intent to show nuclei, has a similar 'rpoblem' The birefringent pieces (that are also sensitive to orientation as shown by the full wave plate) are I'm sure broken pieces of the lignified bands that are reinforcing the locule-wall - tensioning it in preparation for the opening of the locule and consequent 'peeleing-back' that scatters the pollen or at least fully exposes it to pollinators.

Given that both slides have a very similar-looking problem, I would say that they are probably as you say poorly made - as the presence of the pieces in the anther slide would be a strong indication of a slide that hasn't been rinsed completely (of unattached debris) prior to staining - usually a water or alcohol rinse in preparation for staining will clean away any and all such debris. However, this may be the same cause as the creature slide but I doubt it as I'd expect the 'innards' to remain inside said creature during processing....
That said, my personal thought would be that the slides have been 'squashed' (which only has to be to a degree of a few microns to do the damage - permanent mountants stay more or less liquid for a long, long time post mount) at some stage, perhaps by an objective touching the coverslip, very likely by over-enthusiastic cleaning with a cloth, or simply handling in use or tramsport/packaging.

I'd agree that the pollen/anther slide is of low (rather than poor as it's very likely made to a cost) quality, I'd give it a 4 out of 10, given the use of a single stain when a good counterstain to the (here overstained) nuclei would have produced good contrast and have picked out the cell walls far better, in a different colour of course. In fact I'd have use safranin which would have stained both the nuclei and the lignification, and perhaps fast-green for the non-lignified cell walls and cytoplasm of the pollen-grains.

Do you routinely 'polish' your slides with a soft cloth, or place them on top of each other perhaps when looking at a selection? If so this would be my best guess to cause, but I suspect that you know better than to do that.

[apochronaut]

You may have it, John.
I always thought it was condensed solder flux or cigarette smoke drifting over from either the other side of the factory floor or the gambling table just over yonder , near the privies.

[PeteM]

Hans, I've seen the same thing - tiny bright flecks - with crossed polars and cheap prepared slides. Very annoying, since I try to equip most scopes with simple polarization.

Pretty sure it's in the mounting medium.

What was a surprise is that I recently bought multiples (25-50) of the exact same slides to give as handouts to kids - things like onion root tips showing mitosis - and there are significant differences in how much of this shows up from slide to slide in the same batch (same subject, same supplier). I suspect it must be something crystallizing (or not so much) out of the mounting medium?

[hans]

I checked more of the slides and similar stuff is in all I looked at. In all cases it it very transparent and uncolored in brightfield but strongly birefringent. It also shows up evenly across the entire area of mountant, not just near the specimens.

Do you routinely 'polish' your slides with a soft cloth, or place them on top of each other perhaps when looking at a selection? If so this would be my best guess to cause...

I do actually, fairly frequently, to remove all the dirt and fingerprints left over from handling by a three year old, which I why I did not invest a lot of money in high-quality slides. But I just did a quick experiment laying one flat on the table and applying as much force as I could with my thumb (both straight down and shearing) and did not notice any change, so they seem to be fairly robust.

...but I suspect that you know better than to do that.

Not a safe assumption, especially when it comes to biology and traditional microscopy...

I always thought it was condensed solder flux or cigarette smoke drifting over from either the other side of the factory floor or the gambling table just over yonder , near the privies.

I do wonder what these high volume, low cost slide manufacturing operations look like. I understand there are some fairly automated sectioning/mounting systems used for cancer diagnosis, I think? Probably too expensive to use on the tilia plants, housebees, and rabbit and dog parts.

Pretty sure it's in the mounting medium.

Perhaps the mounting medium comes in granular form and this stuff in not completely dissolved before use?

Something else I noticed -- in this one whatever chemical was on the specimen when it was mounted appears to have cause the granules to clump together near the specimen. Far from the specimen it looks uniformly like the finer-grained part on the right side of the image.

[Scarodactyl]

Epoxy can sometimes crystallize. I've seen it from my own mixing and on the insides of a pair of nikon doublets, though I am not sure what's actually forming. I wonder if that's what you're seeing here.

[Greg Howald]

That graininess is caused by using a cheap mounting medium.
I purchased a lot of slides from different manufacturers.
The less expensive slides are fine in bright field but the graininess appears in dark field, Rheinberg and XPL and sometimes oblique lighting.
I started cleaning things when it it first happened to me and when I finally figured out that the problem was a particular set of slides I disposed of them and chalked it up to experience. I decided that If I was going to purchase prepared slides I'd have to get out my wallet.
Companies like Carolina Science or Wards will honor your purchase if you have a problem and take corrective action.
Greg

[hans]

Apparently this is not uncommon. Any idea what the cheapest viable mounting medium is? Seems like epoxy, in general, tends to not be the cheapest option, so probably not used in the lowest-grade slides?

[Greg Howald]

Mounting medium may be acetone or lacquer based. Graininess I have accidently created may also be caused by drying or curing slides at too high a temperature. Quick evaporation at high temp would undoubtedly cause the problem.
Greg

[hans]

In any case, as a longer-term solution to the slide quality problem (or maybe not, matching even low-quality professional slides sounds fairly challenging) I have been reading some of John's past threads, and have a couple recent eBay purchases that still need to be sterilized before bringing them in from the garage: