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Specific Gravity and Absorption of Arks vs Washita's

Here are some comparisons of SPG's and ABS of a few stones of mine. They were not run in a laboratory, I just made do with what I had at home. I am pretty close on the numbers though and I think it's interesting how the stones differ.

The Washita's are vintage stones that had been degreased. I believe they are pretty clean though as I had another soft Ark that I thought had never been used and I found out different when I dried it in the oven and oil came to the surface. None of the Washita's did that and Dan's stones used here have never been used with oil.

My absorption numbers could easily be off a tenth or two as my scale isn't that fine and it's hard with such a small sized sample but still trends are apparent.



Washita 1- SPG -2.289 - ABS 1.0

Washita 2- SPG- 2.268 - ABS 1.1

Dan's SFT- SPG- 2.321 - ABS 1.9

Dans HRD- SPG -2.466 - ABS 0.8

Dan's BLK- SPG- 2.700 - ABS 0.2
 
What method did you use for the spg? I did a quick test with a tray on a scale filled with water and suspended the stones in the water way lol. Will do a better test this week, and of all my stones, but my initial result after three weighs and suspended weighs was my black was 2.65 and my black translucent was 2.60. completely different and finer look though .
 
  • Re-weighed all my stones. Here are my large stones. Nw black is 1372grams /515 =2.664. Nw trans black is 1335/503=2.564. Dan's soft is 757/322= 2.351 I weighed each measurement three times, the NW are new the Dan's I have used three times with a weak 1/4 ballistol to water mix.oh and my mystery turkey washita is 608/260 for 2.338. I used a digital scale good to 30lb measuring in grams, check accuracy with a 100 gram weight from some old triple beams that are to small for this adventure. It was spot on. I know some have a greater variance the heavier they weigh so ymmv.
 
@GeronimoWSB Are you weighing and then getting volume from dimensional measurements? I can see how using dimensional measurements vs water displacement could give very different specific gravity results.

Edit; Ah, pardon me, I see my concerns are exactly what is being discussed. My bad. I'll move along and read the previous posts.
 
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@GeronimoWSB Are you weighing and then getting volume from dimensional measurements? I can see how using dimensional measurements vs water displacement could give very different specific gravity results.

Edit; Ah, pardon me, I see my concerns are exactly what is being discussed. My bad. I'll move along and read the previous posts.
First weight listed is on the scale next is suspended by fishing line in a container of water not touching any sides or bottom. No problem. My new black trans is completely different than the black in looks, going to flatten and Lapp them this week. They are slightly off. The black looks grey until it gets wet , then jet black.
 
First weight listed is on the scale next is suspended by fishing line in a container of water not touching any sides or bottom.
With this method couldn't a very porous stone, that could easily absorb water to displace the air, and was pure silicon, have the same SPG as a non porous stone of pure silicon? It seems to me that a volume based on the dimensions of the stone has to come into play. Or maybe wrap the stone in plastic wrap, so that the buoyancy of the air would show up.
 
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I am sure there are ways to 'cheat' but Arkansas stones are pretty dense and their moisture content have been listed in old books from freshly mined to dried examples. But a very porous stone absorbing water definitely would show up compared to a non porous stone in being weighed in water. Ark's look to dry fast because they don't absorb water imo, my scales barely moved a gram over several stones showing they didn't absorb water quickly. If you want to see an easy example get a small marble unsealed square and pour a small amount next to it. It acts like a sponge , novucalite (sp) doesn't do that
 
I am not an expert , just here to learn btw, so if you figure out I am wrong on anything it's fine. Just trying to put numbers to anything to learn.
 
With this method couldn't a very porous stone, that could easily absorb water to displace the air, and was pure silicon, have the same SPG as a non porous stone of pure silicon? It seems to me that a volume based on the dimensions of the stone has to come into play. Or maybe wrap the stone in plastic wrap, so that the buoyancy of the air would show up.
There are permeable and impermeable pores in aggregate, so the answer is a porous stone could not have the same SPG as a non porous with all other make up being equal. The test method I loosely followed calls for immersion in water for 15-19 hrs. This gives an SSD weight that can be used for calculating absorption. This read could answer some of your questions.
https://www.in.gov/indot/div/mt/aashto/testmethods/aashto_t85.pdf
 
A porous stone that doesn't instantly absorb enough water to fill the pores could throw this test method out of whack. Same for an oil soaked stone that is repelling water. Washitas for instance. I read a geological report some time ago regarding their difference in weight when freshly mined and after being dried; it was significant - something like 6% as I recall for the more porous stones. So that test method is something that would definitely need to be followed to get a chance at accuracy. With an old oil-soaked stone that test might be inaccurate no matter what.
 
Ya, there is plenty to go wrong and with running these at home, it's probably best to just compare the stones against each other from the same tester to see how they compare rather than comparing the data side by side.
 
I just received a soft ark and hard ark from natural whetstone, and the hard ark seems to absorb more water and hold on to it much longer than the soft ark. I'm curious as to why the supposed finer grit stone absorbs water so quickly? These may sound like stupid questions, but can a more porous stone still be finer, or does porosity even have anything to do with determining grit rating?

I've been away from B&B for awhile, glad to see all of you are still here discussing such things!
 
Denser stone should have less absorption. I think some other factor is coming into play, maybe the surface finish. The numbers I got with Dan's soft Ark I suspect are to high because one side of the stone is as received and has never been used or lapped.
 

kelbro

Alfred Spatchcock
Surface tension of the water should be overcome with something like a drop of dish soap to keep from skewing the data.
 
Both of the soft and hard arks were finished on the same lapping plate, and their surfaces feel and look (held up to a light) almost identical. I emailed natural whetstone with inquires as to why they were so close (according to my rudimentary tests) in grits. Maybe my soft ark is on the hard side and my hard ark is on the soft side.
 
Both of the soft and hard arks were finished on the same lapping plate, and their surfaces feel and look (held up to a light) almost identical. I emailed natural whetstone with inquires as to why they were so close (according to my rudimentary tests) in grits. Maybe my soft ark is on the hard side and my hard ark is on the soft side.
I took it for granted that we were talking about a black hard Ark. Not sure why I thought that, maybe not the case? Isn't that also the company that sells a black that isn't as dense?
 
Not sure about the less dense black. I know natural whetstone is where Jarrod from TSS gets his Arks from that he makes convex.
 
Maybe I had them confused with the Dunsten black. I see their prices are pretty good but I have no experience with their stones. Is yours a combination stone?
 
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