On August 25th, I wrote about measuring DE blade width with a digital caliper and a homemade cardstock fixture ([thread]499240[/thread]), and on September 1st, I started a thread about a comprehensive DE razor blade table in the B&B ShaveWiki that would hopefully have enough room for all blade measurement data, including blade width, thickness, etc. ([thread]499764[/thread]): Blades are either new or used. Ideally, only new blades should be used for official blade measurements. Used blades might have buildup on them that is hard to eliminate and might affect thickness measurements, for example, and more importantly, used blade width might be a little less than new blade width due to wearing down of the cutting edges. If dimensions do not measurably change by normal use or by time in a blade bank, then used blades could be treated like new blades for official measurements. I was guessing that I wouldn't be able to measure any differences, but I wanted to confirm this guess, so I conducted a small experiment. I measured the thicknesses and widths of one new KAI Stainless Steel blade and one new Polsilver Super Iridium blade before using them for 6/7 and 5 shaves, respectively, after which I measured their thicknesses and widths again. Wax spots were thoroughly removed from the Polsilver blade. (KAI blades do not have any wax on them.) Blade thickness was measured first with my digital micrometer, having a resolution of 0.001 mm. Blade width was measured next with my homemade cardstock fixture, to properly hold the blade, and my digital caliper, having a resolution of 0.01 mm. Before measuring the blades, both when new and used, the blades and measuring faces of the digital caliper and digital micrometer were properly cleaned with paper soaked with rubbing alcohol and allowed to dry. Room temperature was very similar during all measurements. Here are the thickness and width measurements: BladePurchase DateMeasurement DateConditionThicknessWidthKAI Stainless Steel2016-07-122016-08-26New0.100 mm22.16 mmKAI Stainless Steel2016-07-122016-09-03Used for 6/7 Shaves0.100 mm22.16 mmPolsilver Super Iridium2016-07-242016-09-03New0.091 mm21.97 mmPolsilver Super Iridium2016-07-242016-09-08Used for 5 Shaves0.091 mm21.97 mm As you can see, the width and thickness measurements are identical before and after each blade was used. This was expected, but it was better to confirm the suspicion than operate in the future under an assumption, if used blades are ever to be measured. It is very possible that blade width might measurably decrease with significantly more use, such as when used dozens of times by an Excalibur Club member. Given the results here, one could argue that it would be cost-effective to break into blade banks and measure blades that were used normally. I prefer to err on the side of caution and consistency and stick with only new blades as the best practice for collecting official blade dimension measurements. Nevertheless, both new blades and blades that were used normally could be measured and collected together, as long as all pertinent information is noted. Purchase date, for example, is important to record because blade measurements could be found to have changed due to design and/or manufacturing differences. The measurement date and condition of "new" or "used" should be enough for blades that are new and then used normally and measured soon thereafter, but for used blades from a blade bank, it would be preferable for some estimate of when the blade was used to know how long it was sitting around before being measured, but such estimates might be futile and unnecessary.