Specific Gravity, What is it Good For?
Absolutely Nothing, Say it Again….
Stardate - March 10 2024
Over the last decade or so, many internet platforms have become breeding grounds for toxic egos searching for deeper and deeper layers of minutia to weaponize. The nauseating manhood measuring nonsense never ends. First it was microscope photos proving who hones the best and after that it was game-on for the testosterone Olympics. Let’s get real here please. We are shaving. Put the SEM down.
The title is a tongue in cheek reference to the obsessive focus some people online has put on SG in recent times. Of course SG is a useful and valuable specification when used correctly. Judging an Escher vs an Ark based on SG is ludicrous though. And judging stones based on SG without factoring in other very pertinent data is equally ridiculous. Trying to compare household SG to numbers collected by a verified lab doesn’t make much sense to me.
Way I see it, a hone either hones or it doesn’t. Measuring SG doesn’t tell you whether the stone hones or how well it hones. It won’t tell you what the stone is or is not. It’s just a scrap of data used by scientists when compiling lists of data for the purpose of reviewing metrics, analytics, etc.
Impurities in stones will throw off the measurements. Kitchen table laboratories are not going to provide the environment needed for accuracy. Sure, I can measure SG and get some sort of number to put into a list. What does that list do for me though? Am I a geologist, do I have a sample size of hundreds of stones all measured in the exact same set up by the same person with myriad checks and balances to ensure a high level of consistency and accuracy?
So, yes, measuring SG can be fun. But numbers collected by people in their bathroom counter across the world, using kitchen scales bought on Amazon, without adhering to even the basic parameters of temperature for establishing SG… they’re not that useful.
SG, in the world of Novaculite, here in the USA, is used to gauge density and ‘hardness’ of the stones. These numbers do not relate to other stones quarried elsewhere. A Translucent Ark from Hot Springs Arkansas with a SG of 2.7 is not necessarily going to be better or worse than a slab of Novaculite from any other part of the world, regardless of what it’s SG is. And if we are trying to compare to a different type of stone, mineral, etc., then there is even less of a point to the numbers. Slate can have a much higher SG than Novaculite and be useless as a sharpening stone. Novaculite is a type of Chert, sort of, but there really is no one single absolute set of parameters defining it. Novaculite is, essentially crypto and micro crystalline quartz but percentages of that quartz and the presence and/or lack of impurities, and which impurities, varies tremendously.
In the world of rocks and minerals, Mineralogists and Geologists do not agree on terms quite often. If you take a thin section of a Charnwood stone, and compare it to one from a Translucent Arkansas stone, you see they are not identical yet they are both ‘classified’ as Novaculite sometimes. Science is great but to understand some subjects like this one, it requires a deeper understanding that google fu and forum wisdom is going to provide.
Necessary Side Bar - Novaculite, the Noun
Arkansas Novaculite is its own ‘thing’, in many ways it is a distinct mineral. The term was first used by Griswold back in 1892. In those days, it was widely accepted that Arkansas Novaculite was a superior sharpening stone to the venerable Turkey Stone, Charnwood, and other similar types of whetstones. The content of ‘Arks’ was tested and reported to be finer and more consistent and pure. Those qualities were found to improve cutting speed, and edge refinement capabilities.
However, the first known or recorded use of the term “Novaculite’ was by Kirwan; he used it as a class name for stones, not a type of mineral. KIrwan did not create the name Novaculite out of thin air. One of his predecessors, Lefke, referred to such stones as Novacula - Latin, for Razor Stone, or stones used to hone razors.
Kirwan’s very first reference, in the first edition of his book on Mineralogy, for Novaculite was for a specimen of ‘Turkey Stone’. Kirwan had this stone listed as argillaceous and not siliceous. In Kirwan’s first edition he also referred to several other stones as being in this class, but the descriptions were somewhat rudimentary. Some refinements appear in later editions. At the time Kirwan authored his book, The science had not progressed to the point where micro and cryptocrystalline quartz was known and understood. But it was known that certain stones could whet a razor correctly. And so it goes.
The science of mineralogy has always been and still is a work in progress. There is no one single ‘true’ novaculite; since day one the term is more conceptual than anything else. Kirwan was referring to stones used for sharpening razors and not an exacting chemical or crystalline composition. Mineralogy was in its infancy in those days and Kirwan’s study and use of Specific Gravity helped form part of the basic foundation.
Back to Specific Gravity
There are several ways to determine SG. The most popular method is usually not considered to be any of the most accurate methods. The hone gurus usually weigh the stone dry, then weigh the stone suspended in water. The tub of water is zeroed to start, then the stone lowered on a string until it is submerged but not touching the sides or bottom of the tank. The weight of the stone suspended in water, in grams, is recorded and divided into the dry weight of the stone also in grams. The resulting number is an approximation of the sample’s SG.
In the set up pix above, the SG maps out to 2.655, 77/29 = 2.655. The number is meaningless because it is Coticule glued to slate. In theory the weight of thread used to suspend the stone factors in. Removing the .05 g from the equation brings the number to 2.659.
With Arkansas stones, the guidelines for Soft/Hard/Translucent are pretty close together. Quarries do not test every stone, they rely on experience and how the saw cuts the stone to know what’s what. A hard Ark can be SG 2.6, and so can a Translucent. Some Translucent are 2.7 but they might not perform better than a black Hard Ark with a SG of 2.5. If you sit down and do the math, you’ll see how a minuscule difference in density/weight can change the stone’s position on a list.
A hematite inclusion can raise SG significantly. An air pocket or fissure can lower it. If your Ark read 2.4 you might have a Washita but it could also turn out to be a Soft Ark. Modern soft Arks sold as Washita may have low SG but aren’t really Washita when compared to the Washita sold by Pike back in the 1920s or Norton in the 1930s through the 50s. Back in the early 1900s, Washita and Arks were sold by weight per cubic foot. The most expensive was the harder stones because they took more time, effort, and investment to cut.
So, when you read some content on the internet about stones having this or that Specific Gravity, take it in stride. If you decide to measure your stone’s SG don’t worry about how your number compares to someone else’s numbers for a different stone measured by someone else in a different place at a different time using different gear. Most kitchen scales are not that accurate and can easily be off by a couple/few grams per lev of material. I would suggest to use whatever numbers collected as a guide to compare your own results when weighing other stones; same time, same set up, same gear, same place, etc. But keep an open mind because we don’t sharpen razors with excel workbooks, lists, numbers, or theories fabricated by egos trying to go viral on whatever the social media platform of the day is.