Yellow Slides

[apochronaut]

Just about all the slides I have ever had were green or blue green if I look through the edge. I also have about 10 that are yellow. I know that old glass can sometimes be sun charged to turn a bit yellow but these have been in a box. Is it impurities, or is there a different kind of glass that is yellow?

[dtsh]

The only glass I've seen which yellows is stuff that was made with arsenic which can yellow from exposure as you've mentioned, but I believe the use of arsenic dropped off around WW2.

I've heard that some glasses contain thorium and it will yellow with time and apparently can be reversed by exposure to UV; no practical experience here, just repeating what I've encountered. If you've got a UV light perhaps test a slide under it or in a sunny window sill?

[MicroBob]

Hi Phil,
I think Borosilicate glass is neutral or even yellowish in colour. Today I'm not aware of a source for slides from borosilicate glass. There are slides named "Duran" but they are soda lime glass, albeit a better kind. Could you try to find out if your slides are made from borosilicate glass?
For long term storage borosilicate slides would be ideal, but noone makes then as far as I know.

Bob

[apochronaut]

Lower coefficient of thermal expansion. Possibly for use on a hot stage?

[Chas]

I thought that I once had some BDH borosilicate glass slides... but looking in a 1993 catalogue I cannot see that they sold them (then)
However their coverslips were borosilicate, so perhaps that is the source of my confusion(?).
There seem to be low-iron clear glass slides (like the BDH Super Premium) eg:
https://knittel-glaeser.com/products/microscope-slides/
I cant think that I have noticed yellow glass slides though.

[apochronaut]

Thank you for that link. It seems that sulphur impurities , might be the cause of yellow soda lime glass but calcium if it is borosilicate.

The Knittel page does suggest that they normally use low impurity soda lime glass but that they do also make custom formulation slides. Maybe you ended up with some borosilicate from them?

I have been doing a bit of research on glass in order to solve this riddle and came across a class action lawsuit vs. World Kitchen (Corelle), over exploding pyrex bakewear. It seems that PYREX labwear is still made by Corning but Corelle /World Kitchen was spun off in 1998 as a consumer products division and they make the kitchen stuff. PYREX was originally borosilicate glass but since the spinoff and a bit before, pyrex bakewear has been made from tempered soda lime glass. The borosilicate products are PYREX with all upper case letters, the soda lime pyrex are lower case. There is another differerence too. The colour. A pyrex measuring cup has a decided blue tint when looking horizontally through it's bottom. A PYREX cup bottom is clear. There have been some pretty nasty shatters.

[MichaelG.]

That pyrex cf. PYREX issue is interesting, and very worrying … thank you for mentioning it.

MichaelG.

[apochronaut]

The licensee making PYREX kitchenware for the European market still uses borosilicate glass.

[Hobbyst46]

Labware

So I looked at the following slides at my disposable:
- Starfrost 1mm ordinary slides
- Superfrost 1mm ordinary slides
- 5-marked white circles (sort of very shallow wells"), 1mm slides from PGC Scientific (30-40 yrs old)
- Well slides, thickness 1.4mm, from India

None of them is marked as borosilicate or similar.

The first four types are colorless or very nearly so.
The well slides are definitely green, IMO not due to their being thicker but because they are made of iron-containing soda glass.

I look at an original 10mm diameter PYREX (u.s.a.) Petri dish. Colorless no matter what viewing angle.
I also look at an unbranded beaker, marked "boro 3.3". Colorless no matter what viewing angle.

Kitchenware

Many years ago there was also Duralex. They were heat resistant, yet scratchable, so relatively soft. When such a saucer hit the floor at the proper angle it would shatter into hundreds of tiny fragments. Similar to PYREX kitchenware. And unlike any soda-glass kitchenware, that breaks into large fragments, mostly.

FWIW.

[apochronaut]

Yes. Duralex i have seen and broken was from France. Yes. lots of tiny frsgments. There was also Fireking in N.A. , made by Anchor Hocking, which has clear glass.

The exploding into tiny fragments phenomenon is likely due to internal pressure. It is explained by the Prince Rupert's Drop. I made the mistake of drilling into a tempered glass shelf once and it exploded like Duralex.

https://youtu.be/xe-f4gokRBs

[deBult]

The licensee msking PYREX kitchenware for the European market still uses borisilicate glass.

Thanks, we have a few over here, made in France, PYREX in large letters and clear glass when you look through.