What does this blue square on my volumetric flask mean? I see such squares/rectangles on a numerous other flask brands as well. What is its purpose?

Volumetric flask, 100 ml, Class B, Blue, Eisco Labs

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    $\begingroup$ Most glassware has such stuff I guess it is a brand marking. $\endgroup$
    – user145852
    Commented May 20 at 4:25
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    $\begingroup$ Well, you can check this out: borosillab.com/volumetric-flask It explains all the other markings on a branded volumetric flask. If you look closely, there is a smaller solid coloured rectangle, above the "standard" sign. Perhaps it is present there on that flask to show the colour used for all the markings made on that flask. Or it might just be there for aesthetics/design. On other glassware, where the same box is larger and white(light coloured), I have seen people use it as a label as well. $\endgroup$
    – Ronith
    Commented May 20 at 4:51
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    $\begingroup$ This matt-finished area — here likely enameled, but could also be sandblasted or etched (like the graduation mark is) — is for marking, normally with grease pencils. The background color makes sure your markings are visible regardless of how clear or dark the solution inside the flask is. Has nothing to do with branding, unless a manufacturer takes a deliberate design choice shaping this area after their logo, which I don't see here. $\endgroup$
    – andselisk
    Commented May 20 at 5:22
  • $\begingroup$ @Krishna The «eisco» only indicates a brand, similar to the spades / pique symbol on ACE glassware (example which for some reason entered into the template library about glass utensils in ChemDraw (can be removed, though) and sometimes even is seen in the (graphical abstracts of) publications, e.g. here, or here. So far I didn't see Corning, Schott, chemglass etc similarly advertised in papers... $\endgroup$
    – Buttonwood
    Commented May 20 at 9:44

2 Answers 2


The etch mark truly could be blue (or in an other color). But (arguably) it is more common to find such an etch mark in plain white on glass ware, for instance beakers, or flasks, or bottles, or round bottom flasks. So it is not that particular to a volumetric flask, nor to the supplier. It is possible the picture was edited for higher contrast, such that the white marks now appear a bit blueish but are easier to read, too.

In addition to @andelisk's comment, you can write on this spot with a pencil you already carry into the lab (think e.g., marking TLC plates' start/front line & spots) to briefly tag a container. Different to a label, it is quick; in contrast to a sharpy (or other marker pens), it does not come off that quickly when some drops of iPrOH, acetone or other solvent run over. But don't forget to erase it (a soft rubber hose/the stop cock [e.g., of the NaOH bottle] is a quick approach) prior to putting the container in the washer (because its drying cycle makes it more difficult to subsequently get the etch mark clean again).

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    $\begingroup$ From my experience an ordinary pencil barely leaves any marks on enamel. A Sharpie's colorant can sometimes be hard to get rid of since it gets partially adsorbed. So, I stock up on Stabilo-All multi-surface pencils, which are pretty much a "civil" version of old heavy-duty grease pencils. $\endgroup$
    – andselisk
    Commented May 20 at 11:44
  • $\begingroup$ Depending on the brand, I agree these fields can be very glossy and smooth; easy tangible higher in level (compared to the wall of the container) when gliding a finger across the marks. Like a thick blot of paint. And with other brands, these fields are more coarse, and hence easier to write on with a pencil though they are not the (somewhat translucent) spot of a borosilicate glass touched/partially eaten away by HF. $\endgroup$
    – Buttonwood
    Commented May 21 at 18:00

One of the ASTM International requirements, formerly known as American Society for Testing and Materials, is:

ASTM E288 - 10 Standard Specification for Laboratory Glass Volumetric Flasks.

4.5.3 Laboratory Marking Spot — Each flask shall have an area roughened by blasting or enameled to provide a suitable area for laboratory marking.

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

This is from 2017. The blue spot is meant to fulfil this criterion. These standard documents are relatively expensive to buy but most good university libraries should have access if you are interested in details. However, this "spot" shape, color, etc. is not uniform. One can find countless volumetric flasks which do not have such markings, especially in older flasks.

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    $\begingroup$ An interesting read for the comparison to ISO 1042, I added a +1. Because labbox.eu provides a data sheet about volumetric flasks reading (page 3/12) «Volumetric flask class A according to USP with individual certificate [...] Designed according to ISO 1042, DIN 12664 and USP standards. [...] USP standards are more accurate than ISO 1042.» (emphasis added). $\endgroup$
    – Buttonwood
    Commented May 21 at 18:19

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