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On the Measurement of Croap Durometer: A New Methodology

What about the Archimedes principle?

Harder soaps will be denser. Thus, if you add identical masses of different soaps to a full bath, you can calculate density by the amount of water which spills into the flat below you.

An added benefit is that you can quickly detect gold and other precious metals which are often hidden in croap.
 
What about the Archimedes principle?

Harder soaps will be denser. Thus, if you add identical masses of different soaps to a full bath, you can calculate density by the amount of water which spills into the flat below you.
This is a fascinating idea! I'm very familiar with the principle, and as a scientist I've been delighted to see it's application in the popular media:



The logic of submerging ducks and witches is well established in the literature, however it's first necessary to ascertain the volume of the object under measurement. This is true of croap/soap as well. Robinson observed in 1873 that bath measurements of volume could vary as a function of one's dinner and in the even of flatulence, the underestimation could be quite considerable; in the present case it, could easily overshadow the volume of a puck of soap or a clump of croap. How would the volume of croap/soap be measured precisely enough to overcome Robinson's principle?
 
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@ShavingByTheNumbers

This problem seems like it would be right up your alley. Any ideas on how to accurately measure the firmness of croap in a repeatable way? Here are the requirements:

  1. Measurement should be on an interval scale (not ordinal or nominal)
  2. It must use only household materials costing in total no more than $1.00
  3. It should be possible to make the measurement apparatus in less than 5 minutes
  4. Individual measurement should take no more than 10 seconds
  5. Accuracy must be +/- 13.7%
Hey, Nick! You started a very interesting discussion! Measuring croap hardness is no easy task. Good ideas have been discussed here. I've never thought so much about measuring hardness. I've learned how expensive durometers get for softer materials, so I understand why a OOO durometer would be off the table. Nevertheless, it is smart to try and follow established standards.

The O and OO durometer types use an indenter with a 1.20 mm spherical radius, but it looks like the spring stiffness drops by over 7X from O to OO. In going from OO to OOO, the spring stiffness remains the same, but the indenter spherical radius increases by over 5X to get to 6.35 mm. The OOO-S durometer type, for even softer materials, increases the spring stiffness by under 2X, but switches the indenter to a 10.7 mm radius disk to increase surface area and decrease indentation pressure.

The OOO and OOO-S durometer types are probably the most applicable for croaps. You might be right that OOO would be the most appropriate. I would try to mimic the measuring apparatus and method. The indenter tip would then be a readily available ball akin to OOO or a readily available disk akin to OOO-S. Making anything with a spring would be unreasonable, so measuring force could be done with an appropriate scale for static or quasi-static indentation, as has been suggested here. A drop test was also suggested, but dynamic testing violates standard hardness testing procedures that often involve maintaining a reading for some seconds.

It doesn't seem to me that you'd be able to accomplish your goal without violating design constraint #2. However, the design process is iterative and sometimes design constraints need to be modified to get to the job done. :)
 
Hey, Nick! You started a very interesting discussion! Measuring croap hardness is no easy task. Good ideas have been discussed here. I've never thought so much about measuring hardness. I've learned how expensive durometers get for softer materials, so I understand why a OOO durometer would be off the table. Nevertheless, it is smart to try and follow established standards.

The O and OO durometer types use an indenter with a 1.20 mm spherical radius, but it looks like the spring stiffness drops by over 7X from O to OO. In going from OO to OOO, the spring stiffness remains the same, but the indenter spherical radius increases by over 5X to get to 6.35 mm. The OOO-S durometer type, for even softer materials, increases the spring stiffness by under 2X, but switches the indenter to a 10.7 mm radius disk to increase surface area and decrease indentation pressure.

The OOO and OOO-S durometer types are probably the most applicable for croaps. You might be right that OOO would be the most appropriate. I would try to mimic the measuring apparatus and method. The indenter tip would then be a readily available ball akin to OOO or a readily available disk akin to OOO-S. Making anything with a spring would be unreasonable, so measuring force could be done with an appropriate scale for static or quasi-static indentation, as has been suggested here. A drop test was also suggested, but dynamic testing violates standard hardness testing procedures that often involve maintaining a reading for some seconds.

It doesn't seem to me that you'd be able to accomplish your goal without violating design constraint #2. However, the design process is iterative and sometimes design constraints need to be modified to get to the job done. :)
Excellent points on the differences in spring stiffness and tip tyoes between OOO-s vs OOO durometers. It's unfortunate that they cost $1,000, otherwise they'd be perfect for the job. Too bad harbor freight doesn't make a budget version. :(

What do you think about the idea of using water in a plastic shot glass as a static force cause the penetration of a pin shaped tip that penetrates the soap. That way you could measure the weight of water to necessary on a kitchen scale? Or some variation of the idea using a measurable weight of some kind in lieu of spring resistance?

I agree constraint #2 was probably too restrictive. What do you reckon the right budget is, and what would you propose?
 
@Esox

You're a clever guy with a keen mind for the mechanical; do any ideas spring to mind on how to measure croap "firmess" with a simple homemade tool?
 
Excellent points on the differences in spring stiffness and tip tyoes between OOO-s vs OOO durometers. It's unfortunate that they cost $1,000, otherwise they'd be perfect for the job. Too bad harbor freight doesn't make a budget version. :(
Yes. That is unfortunate. If anyone would have a budget version, it would be Harbor Freight. :)

What do you think about the idea of using water in a plastic shot glass as a static force cause the penetration of a pin shaped tip that penetrates the soap. That way you could measure the weight of water to necessary on a kitchen scale? Or some variation of the idea using a measurable weight of some kind in lieu of spring resistance?
That's not a bad idea, but it doesn't quite follow durometer standards. As I've learned from Wikipedia, since I'm too lazy to get out one of my engineering books, a durometer measures the depth of an indentation created by a specific force for the specific durometer type, which is associated with a specific indenter tip. The material being tested must be at least 6 mm thick. If the indenter penetrates a certain distance (2.54 mm with most durometer scales) or more, then the hardness value for that durometer scale is 0, and if the indenter doesn't penetrate at all, then the value is 100. Trusted values are between 10 and 90, so if that doesn't happen, then a different durometer type should be used. Since you are thinking that the OOO durometer would be appropriate, wouldn't you then try to use the same indenter shape with a spherical radius of 6.35 mm? The prescribed (spring) force is 1.111 N (0.25 lb or the weight of 113.3 grams in standard gravity). That is the weight of about 20 quarters (USD). I'm sure that the indenter would reach maximum indentation with some croaps, leading to trying the OOO-S scale with its 10.7 mm radius disk and different force and maximum penetration. Varying the force to achieve a desired indentation with any given durometer type is fundamentally different, but you might be able to determine some sort of approximate equivalence.

Would it be possible to approximately match the defined durometer forces and indenters while figuring out indentation, and hence, hardness, with a reasonable resolution/precision and without breaking the bank? I think so. The homemade durometer in my mind would work. Measurement of indentation distance wouldn't be perfect, but I think that it would be okay and there would be more than one measurement method available. Also, if materials were sourced so that consistency among users were not a problem, then users wouldn't need a scale.

I agree constraint #2 was probably too restrictive. What do you reckon the right budget is, and what would you propose?
I wouldn't constrain the cost. I'd just work on accomplishing the goal of a homemade durometer for measuring croap hardness that is reasonably simple and meets measurement resolution/precision while getting the most performance out of the cost.
 
Scrape the surface once with a teaspoon (quite hard).

1. If you get a full spoon it’s a cream
2. If you get shavings it’s a hard soap
3. More than shavings but less than a quarter teaspoon it’s a soft soap
4. Anything else, a cramp of some description.
 
If I could think of a way to do that I could also measure the rigidity of a loaded blade in a razor.
@ShavingByTheNumbers

Holy cow. I just realized that measuring rigidity on a blade is exactly the same problem as measuring croap firmness.

We're basically just measuring the force required to cause deflection of the material under measurement.

That means that blade rigidity can be measured very precisely. The tool for the job is a Type D durometer. It uses a spring force of 44.45 Newtons, which should be enough to cause blade deflection. Basically, you would measure how many N it takes to cause separation between the blade and the top cap. Easy peasy!

The mechanism is simplicity itself. Here is how the mechanism works:



Here is a nice one for $27 from Amazon. We should have a BOSC bake sale and get one for sciencing:


 
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I'd just work on accomplishing the goal of a homemade durometer for measuring croap hardness that is reasonably simple and meets measurement resolution/precision while getting the most performance out of the cost.
Making anything with a spring would be unreasonable,
Lol. I just figured this out too. I figured out how to build an actual spring loaded durometer in under 2 minutes, for less than $1, using parts every person has in house, that has a working scale interval scale. Impossible to say if it's +/- 13.7% accurate without a $1,000 Type OOO durometer though, but it should be very accurate.

I'm going to test 4 soaps that I have of 4 different levels of firmness:
  • Stirling Arkadia (soft croap)
  • Stirling Agar (medium croap)
  • Stirling Haverford hard croap)
  • Arko (soft soap)
I'll be back soon with pics and results. You're gonna laugh when you see it!
 
Good to see you around again Grant! @ShavingByTheNumbers
Thanks, Mike. I stop in now and then, and if called to action, I try to help. :)

@ShavingByTheNumbers

Holy cow. I just realized that measuring rigidity on a blade is exactly the same problem as measuring croap firmness.

We're basically just measuring the force required to cause deflection of the material under measurement.

That means that blade rigidity can be measured very precisely. The tool for the job is a Type D durometer. It uses a spring force of 44.45 Newtons, which should be enough to cause blade deflection. Basically, you would measure how many N it takes to cause separation between the blade and the top cap. Easy peasy!

The mechanism is simplicity itself. Here is how the mechanism works:



Here is a nice one for $27 from Amazon. We should have a BOSC bake sale and get one for sciencing:


A durometer doesn't supply a perfectly constant force, but it supplies an approximately constant force as I understand it from what's on Wikipedia. What is measured is the displacement, usually up to 2.54 mm, which is translated to hardness on a scale of 0 to 100. If only one durometer were used for measuring blade rigidity, then you might be able to get the displacement (up to 2.54 mm or whatever) corresponding to durometer output, but that displacement wouldn't reveal the force that it took to start moving the blade away from the cap.

Instead of a durometer, what one would really want to try is a force gauge/meter. You might be able to get an appropriate one for the task at a good price. However, my thinking is that a force gauge/meter would not be sufficient for getting the job done properly in all cases, possibly even most cases.

Lol. I just figured this out too. I figured out how to build an actual spring loaded durometer in under 2 minutes, for less than $1, using parts every person has in house, that has a working scale interval scale. Impossible to say if it's +/- 13.7% accurate without a $1,000 Type OOO durometer though, but it should be very accurate.

I'm going to test 4 soaps that I have of 4 different levels of firmness:
  • Stirling Arkadia (soft croap)
  • Stirling Agar (medium croap)
  • Stirling Haverford hard croap)
  • Arko (soft soap)
I'll be back soon with pics and results. You're gonna laugh when you see it!
Sounds good, Nick! I look forward to the results!
 
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Behold!!!

I give you the dovometer! Here is a picture of it in the relaxed position with no pressure:



It's a ball point pen, with the spring removed from the bottom half of the pen, and then the spring is inserted into the top half of the pen. The ink tube is then inserted on top of the spring. A millimeter ruler is printed to scale on paper, cut out, and taped on. The firmer the soap, the more mm of spring depression you get.

It actually works!!!

Arko was the first one measured by this miraculous new device (naturally) Here are the first 4 measurements:

Arko: 11 mm
Haverford: 4 mm
AGAR: 2mm
Arcadia: 1 mm

Here is it taking a reading of Arko.

 
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Behold!!!

I give you the dovometer! Here is a picture of it in the relaxed position with no pressure:



It's a ball point pen, with the spring removed from the bottom half of the pen, and then the spring is inserted into the top half of the pen. The ink tube is then inserted on top of the spring. A millimeter ruler is printed to scale on paper, cut out, and taped on. The firmer the soap, the more mm of spring depression you get.

It actually works!!!

Arko was the first one measured by this miraculous new device (naturally) Here are the first 4 measurements:

Arko: 11 mm
Haverford: 4 mm
AGAR: 2mm
Arcadia: 1 mm

Here is it taking a reading of Arko.

VERY COOL! Great job, Nick! It looks like the scale works across the croap spectrum and into soft soaps, too.
 

Esox

I didnt know
Ambassador
We're basically just measuring the force required to cause deflection of the material under measurement.
Yes, but how?

but that displacement wouldn't reveal the force that it took to start moving the blade away from the cap.
I was thinking of something like a preloaded dial indicator but I was unaware of the gauge you mention below.

Instead of a durometer, what one would really want to try is a force gauge/meter.
Here is it taking a reading of Arko.
Yes but, how much pressure does it take to depress it into the soap? Or deflect a blade edge by, lets say, .002"?


Dovometer ™
FTFY :tongue_sm

Now BOSC needs a commercial division with lawyers schooled in patent law haha.
 
Yes, but how?

I was thinking of something like a preloaded dial indicator but I was unaware of the gauge you mention below.

Yes but, how much pressure does it take to depress it into the soap? Or deflect a blade edge by, lets say, .002"?
Fair point. The durometer won't tell you the pressure, but what it will give however is repeatable way of measure relative force required for deflection. An R41 might score a 20 on the 100 point dial, and a Fatip Grande might score a 75 on the 100 point dial.

I don't know how to measure that in newtons, but the key point is that 5 different people could measure those two razors, and the R41 will score a 20 and the Grande will score a 75 for everybody. It's repeatable, and gives a quantitative scale of rigidity. Anybody with a $27 Type D durometer will get the same result anywhere in the world.
 
Just bought a puck of Ach Brito Mogno for $6.00. Absolutely phenomenal soap btw. I noticed that although it's not triple milled, it was quite a bit harder than Arko. It's somewhere between Arko and Williams. I gave it a measurement with the dovometer and sure enough it was. It gave a reading of 18mm. This thing really does work!

I have now measured every soap in my possession with the dovometer, and here are the standings:

Stirling Arcadia: 1 mm
Stirling Agar: 2mm
Stirling Haverford: 4 mm
Arko: 11mm
Ach Brito Mogno: 18mm
 
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VERY COOL! Great job, Nick! It looks like the scale works across the croap spectrum and into soft soaps, too.
Thanks. It does cover croaps and soft soaps, but I can see why there are different Durometer scales for different levels of hardness. Almost all croaps will wind up in the 1mm-4mm range with my dovometer. Really soft croaps like Cella however are probably between 0mm-1mm. I can see the value in having a different scale for these croaps.

The easiest solution is to just reach back into the pen drawer. If you pull the eraser off a standard #2 pencil, and stick the pen tip into it, you've got yourself one penny, standardized probe more suited for softer croaps. :)
 
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