[cyphar]

For more context, sample reference materials from the NIST reference catalogue are not meant to be exceptionally high purity examples of the sample -- SRMs are usually commercially-produced products. The real value is that each sample comes with a datasheet with incredibly detailed and accurate measurements that are (as you said) used for calibration of measuring devices in industrial settings. To quote a Veritasium video about the topic from a few years ago[1], "the thing you're paying for is not the peanut butter, it's the knowledge of exactly what is in the peanut butter".

[1]: https://youtu.be/esQyYGezS7c?t=226

[buildsjets]

Truth. I once paid nearly $500 for a set of 17 certified, calibrated wooden pencils, with documentation showing that each one met their rated hardness levels of 9H thru 6B. And for $500, they don't even come with erasers, that is an added-cost option.

https://www.gardco.com/product/pencil-hardness-test-kit-astm...

[MikeTheGreat]

I'd like to ask a more specific question than my sibling's excellent "Wait, why?" question :)

Why offer erasers on these things? The procedure described below has nothing to do with using these as pencils, and at $500 for a pack I can't imagine anyone, anywhere casually drawing with these.

(Is there another procedure, similar to the one described below, except instead of dragging the pencil tip across a surface you drag the eraser across it? )

[buildsjets]

I’d suggest you read “The TSO’d Pencil” to understand the reference.

Http://www.rstengineering.com/rst/articles/tsodpencil.pdf

[MikeTheGreat]

:)

I had no idea this reference existed, or that it's a a fun, though dystopian, read.

Thanks! :)

[foobarian]

Can I ask why :-) Sounds like an interesting project.

[buildsjets]

The pencil hardness scale is commonly used to assess paint film hardness by checking what is the softest pencil that can mar the surface when you scratch it with a given force. In this case, we needed to assess whether exposure to a certain chemical degraded the integrity of the paint coating that we were counting on for corrosion protection.

[wildzzz]

You use the kit to test the harness of a finish coating, like a paint or a ceramic coating for cars. Pencils have their own hardness scale which can be used to gauge the hardness of the coating. Its really more of a relative qualitative test than quantitative as you'd use this for sample/coupon testing identical coatings. There are more absolute, quantitative methods to measure various hardness characteristics (scratch, indentation, and rebound). Like you'd use the pencil kit on a factory floor to make sure each paint sample performs the same, the sample being a small area on the product or a plate that's painted the same way.

[8note]

the pencil aspect is because its easy for a person to carry and take notes with?

and you dont need to fit the car into a proper harness tester?

[cwillu]

His link includes procedures, which suggest he was testing the hardness of some surface coating or similar:

> For the pencil hardness test, reference ASTM D3363, pencils of increasing hardness values are moved over the surface in a precisely defined way until one lead damages the surface. Surface Hardness is defined by the hardest pencil grade which just fails to damage the surface.

> Observe the pencil track. Sufficient pressure must have been applied either to cut or damage the coating or to crush the lead pencil point.

> If neither coating damage or pencil point crushing is observed, repeat the test until a definite observation is made.

> If scratching or damage of the surface occurs, proceed with the next softer pencil grade and repeat the testing process until a pencil lead grade is found which crushes and does not damage the coating.

> If crushing of the hardest lead should occur, the coating is therefore extremely hard and is beyond the measuring range of this test