Butterscotch

[cotedupy]

I was thinking about this 'Butterscotch' thing the other day, and I came up with a theory that I didn't think had been mentioned before. But reading this thread back, it actually had been. Here's a post of Keith's from a few years back:

I believe thete are a number of possible and actual factors, including oxidation of impurities, presence of oil, actual yellowiish stone due to a natural tint in impurities, sun-turning, and various different combinations of the above.

Because the stone is nearly pure micro/crypto crystalline silica, the effects of light diffraction are going to be seriously amplified - even a teensiest bit of impurity or oil or oxidation could have a major impact on the stone’s appearance. The crystalline structure can act like a signal repeater.

It’s an interesting phenomenon, the ‘antique’ coloring makes for a warm visusl aesthetic. Interesting and functional eye-candy can be fun to have around.

I'm pretty sure that light is the cause of 'Butterscotch' colouration in arks. UV light is a very strong and somewhat weird form of radiation that affects an awful lot of organic and inorganic substances in a variety of ways. And of all the whetstones in the world a Translucent Arkansas - just by it's its nature - is gonna be your most likely candidate.

But UV light isn't the same as visible light, a trans ark might block the former while allowing the latter to pass. We can probably get a reasonable idea though by comparing it to glass, which chemically is largely the same thing (silica) as a trans ark. Normal glass blocks almost all UVB and UVC light, but allows 60-70% of UVA through. I think we can also extrapolate from that, that UVA light does not affect silica, otherwise we'd all have butterscotch windows. But actually impurities in some old glass means it can discolour in light. Apparently it's a bit of a thing in glass collecting circles too:

"Sun-Changed" or Irradiated Glass information from the Glass Encyclopedia

Irradiated Glass: information, pictures and references on glass which has changed colour from radiation or sunlight; brought to you from the Glass Encyclopedia.

www.glassencyclopedia.com

So could UV light similarly affect something else in Arkansas novaculite and cause butterscotch variation? Well let's see... I put a 5p piece on a Washita yesterday and left it in the sun for 5 hours. And even after a short period in (British) sunshine, it has darkened the stone slightly.

Admittedly that still doesn't tell us though exactly what is being 'tanned', and it is certainly possible that impurities in absorbed oil could be the main culprit. But my hunch would be that's it's something within the stone itself. Trans arks absorb very little oil in comparison to any other novaculite, but they pass way more light, and it's in them that we see this colouration most often.

Though I do also have an old Pike LW that's extremely hard, fine, and high SG, that remains a obstinately light caramel colour despite having been degreased probably in total for about 6 months. But the stone, as you can imagine, is also really quite translucent, so again seems to confirm the theory.

Whatever's causing this may be found in certain stones but not others, or it may be possible in all examples. But either way - I'd be fairly confident that 'butterscotch' colouration in Arkansas stones comes from UVA alteration of chemical impurities.

 

[2bit_collie]

Here is my Butterscotch- nowhere near as pure looking as some of the others, but none of the inclusions or pits are toxic. It came with a wooden base that it fits quite snugly into.

 

[duke762]

Scotchy stones rock, just because of their yellowish tint and it's one of the few colors I see well. The mystery of scotchery, may well lie, possibly, in a variance of sg in trans stones or a variety of volatile hydrocarbons that may be fine enough, to penetrate a stones surface well. The stone may have been exposed to these compounds at an earlier time.

As promised here are better shots of my favorite and most beautiful stone from all sides. You can really see how it varies between being a butter scotch, a black, and a standard translucent in these pics. The very dark yellowish butter scotch part is the bottom. It’s an old Pike 8 x 2 by one, and it’s simply stunning.

Cheez and Mice, that is a cool stone.

 

[Gamma]

Every single so-called 'butterscotch' Translucent Ark I have lapped was white as a sheet afterwards and turned 'buttery' again after using oil on it. All of the prattling on about variations in SG, color, etc... meh... seems like a lot of making mountains out of molehills and creating confusion too. I guess it gives people something to talk about or maybe argue about and flex over. If I bought a trans Ark from Dans today and lapped/finished it correctly, it would make just as good an edge as the boxed/labeled quasi-buttery pre-1930s Pike Translucent on my desk right now. Same for the Black Ark from Preyda in the cabinet behind me. SG will be points off in all directions and if I lapped the Pike it would be white as snow; I lapped it when I got it, and now it's 1/2-way back to being quasi-buttery-looking again.
I like the warm tone of the yellowed stones, they have that 'antique' persona to them. Have not found them to be superior in any other way though and I have put a ton of them to test. Many Trans Arks, on arrival, have a really nice working surface from extended use, so that can factor in. Some are a hair faster or slower or maybe a bit easier to get a good finish on after lapping. But when all prep is done equal, at the end of the honing, I find the results are equal. I have yet to find a Translucent Ark that didn't hone as well as all the others I've used. Too many to count..
Washita are another box of tricks - I've had NOS 1950s Lilly Whites that were pure as the driven snow, and others that were so yellowed you'd think they were mined in a urinal. Variation in grain structure with them is really important but being saturated with fats/oils also factors in and that changes color along with cutting personality.

Exposure to light and atmosphere probably also effects on looks/color to some degree; sunlight affects everything it seems. Pollution also.
Long time ago had a huge chunk of Botan that had been stored on a shelf in a laundromat... it's a long story, don't ask, and it had yellowed on one side from being near detergent, and yellowed differently from sunlight on the other side. It also smelled like detergent.

 

[cotedupy]

Every single so-called 'butterscotch' Translucent Ark I have lapped was white as a sheet afterwards and turned 'buttery' again after using oil on it.

Really? That certainly didn't happen when I lapped the one I posted above. At least no more than any other freshly lapped surface looks whiter than stone actually is, because it's reflecting more light than normal.

(I don't think anyone's claiming any kind of meritocratic superiority btw. We're mostly just posting pictures of nice stones.)

 

[Gamma]

Yes, really.
Every one of them became white, then turned back to amber-ish after oil was applied. Even those not lapped but soaked in SG till they were white again turned back to yellowish after oil was applied. Same for freshly cut surfaces. Not a case of one surface reflecting more, or less. It's the surface being somewhat impregnated with oil. Lapping it or soaking it takes that 'film' off, out, whatever. But the creep below the surface can be seen under high magnification. As much as I believe yellow-ish or butterscotchy Trans Arks exist, or could exist, naturally - those I've put to test were not. It's been a decent sample size too.

I've literally had people message me to find out why 'butterscotch' Arks are better...so that buzz does exist, in some form, somewhere. But probably not on B&B though, because, well, everyone here is only posting pix of nice stones....

 

[Empire straights]

I was thinking about this 'Butterscotch' thing the other day, and I came up with a theory that I didn't think had been mentioned before. But reading this thread back, it actually had been. Here's a post of Keith's from a few years back:




I'm pretty sure that light is the cause of 'Butterscotch' colouration in arks. UV light is a very strong and somewhat weird form of radiation that affects an awful lot of organic and inorganic substances in a variety of ways. And of all the whetstones in the world a Translucent Arkansas - just by it's its nature - is gonna be your most likely candidate.

But UV light isn't the same as visible light, a trans ark might block the former while allowing the latter to pass. We can probably get a reasonable idea though by comparing it to glass, which chemically is largely the same thing (silica) as a trans ark. Normal glass blocks almost all UVB and UVC light, but allows 60-70% of UVA through. I think we can also extrapolate from that, that UVA light does not affect silica, otherwise we'd all have butterscotch windows. But actually impurities in some old glass means it can discolour in light. Apparently it's a bit of a thing in glass collecting circles too:

"Sun-Changed" or Irradiated Glass information from the Glass Encyclopedia

Irradiated Glass: information, pictures and references on glass which has changed colour from radiation or sunlight; brought to you from the Glass Encyclopedia.

www.glassencyclopedia.com

So could UV light similarly affect something else in Arkansas novaculite and cause butterscotch variation? Well let's see... I put a 5p piece on a Washita yesterday and left it in the sun for 5 hours. And even after a short period in (British) sunshine, it has darkened the stone slightly.

View attachment 1672353

View attachment 1672351


Admittedly that still doesn't tell us though exactly what is being 'tanned', and it is certainly possible that impurities in absorbed oil could be the main culprit. But my hunch would be that's it's something within the stone itself. Trans arks absorb very little oil in comparison to any other novaculite, but they pass way more light, and it's in them that we see this colouration most often.

Though I do also have an old Pike LW that's extremely hard, fine, and high SG, that remains a obstinately light caramel colour despite having been degreased probably in total for about 6 months. But the stone, as you can imagine, is also really quite translucent, so again seems to confirm the theory.

Whatever's causing this may be found in certain stones but not others, or it may be possible in all examples. But either way - I'd be fairly confident that 'butterscotch' colouration in Arkansas stones comes from UVA alteration of chemical impurities.

Interesting, I have some of the old handmade glass(bubbles in the glass) in my house thats gotten slightly opaque(more cloudy vs a frosted look). It's on the east side of my house and had been taking Texas sun on the nose for over 100 years. The sun here, much like Australia, will absolutly kill you in no time. High uva radiation.

 

[Empire straights]

@cotedupy I've never had a "butterscotch" though for the record.

 

[cotedupy]

Yes, really.
Every one of them became white, then turned back to amber-ish after oil was applied. Even those not lapped but soaked in SG till they were white again turned back to yellowish after oil was applied. Same for freshly cut surfaces. Not a case of one surface reflecting more, or less. It's the surface being somewhat impregnated with oil. Lapping it or soaking it takes that 'film' off, out, whatever. But the creep below the surface can be seen under high magnification. As much as I believe yellow-ish or butterscotchy Trans Arks exist, or could exist, naturally - those I've put to test were not. It's been a decent sample size too.

I've literally had people message me to find out why 'butterscotch' Arks are better...so that buzz does exist, in some form, somewhere. But probably not on B&B though, because, well, everyone here is only posting pix of nice stones....

Mmm, I think that's just how different surfaces reflect light differently.

If you take a block of, say, 'rock salt' - it doesn't look very white. If you grind it up a bit it - it does look white. If you then pour oil on that - it goes back to not looking very white again.

 

[Gamma]

That's not a good analogy, large crystals of sodium chloride can be very clear and translucent. And we're not working with a powdered Silica.

Clear oil on salt doesn't make it look yellow or not white unless it's on top of something yellow or not white. We're looking at a solid piece of silica though, not ground sodium chloride. If you've ever seen a sodium chloride crystal large enough to hold, lets say Halite for example, when cut or polished it's not yellow, sorta clear actually. It can have that white grey translucency though. A polished/lapped surface doesn't change color. Maybe if it was ground it up it might look pure white but if you take a grain and magnify it, the white/grey translucency is still there. I'm not just relying on the naked eye here.

Silica though, whether ground or cut in thin section, it and it's oxides have a particular appearance that's well documented. Yellow isn't in the mix. Impurities exist, and can shift color, or like Citrine the silica can turn yellow from heat and pressure. Here though, the stones in question weren't yellow out of the ground, or heated, and presumably very pure silica given the actual coloring. In these cases, the yellowing was added when in use.

In these cases I am talking about, those I've had on my bench and under my scope, the lapped surface, or de-greased surface returns to it's white appearance. To be fair, the 'white' I have been referring to is actually a greyish/whitish translucent coloring. Not white like a sheet of paper or a typical lower grade white 'hard' Ark.
So, that grey/white coloring was found in the center of the stones I cut, cracked or chipped. It really is the natural color of the stones I was checking in to.

Looking into the exposed surfaces that were cut in section, at roughly 2000x, it is evident that there is a discoloration migrating from just beneath the lapped or de-greased surface, heading toward the middle. Denser at the top, and feathering out, so to speak, toward the middle of the stone. .

When I cut a NOS translucent pike - there was no yellowing anywhere in or on the stone before cutting or lapping or after applying oil. If I had 30-40 years to soak that stone in sperm oil I guarantee it would start to show 'butterscotch' tendencies. This has actually happened with a typical hard ark that was actually white/white before having sperm oil layered on it. It also turned red when I used ATF on it. Different density, but same principal.
There's nothing new about colored liquids staining things.

Checking the coloring of the Trans arks here though, all that was with clear mineral oil so I didn't add color to the equation. The buttery coloring in those stones was definitely added over time by whoever used them. I have to assume it was done mostly by using oil. Atmosphere, UV light, maybe some other stuff added in too. Its feasible that the coloring could be affected somewhat by the boxes they were stored in, like a wood box finished with linseed oil maybe, I had a few of those here actually. Maybe ink from those cardboard boxes outgassed a bit. There are a lot of possibilities.

 

[Legion]

Its feasible that the coloring could be affected somewhat by the boxes they were stored in, like a wood box finished with linseed oil maybe, I had a few of those here actually.

That's a good point I'd not thought of before. Rather than oil put on the stone turning it yellow, BLO, or other chemicals in the wooden box might certainly do that over years. Like oak barrels turning whisky brown.

 

[Legion]

Not that it proves anything either way, but once you crack into them, the butterscotch layer is actually a pretty thin skin.

 

[Pack line]

Isn't sperm oil yellow?

 

[Legion]

Isn't sperm oil yellow?

I believe it is kind of straw coloured. Probably gets browner as it ages.

The old timers used whatever was at hand. From sperm oil, to cooking oil, to old used motor oil. Different oils, organic oils in particular, are going to do who knows what with the addition of time, UV, bacteria, etc. It is only because a trans Ark is so impermeable that we get as little variation as we do.

Most all of the Arkansas I've found in the wild have been black with old oil and swarf. It's that which contributes to the "dirty" yellow staining on the surface mostly, i'd expect. As romantic as we want to make it by calling it Butterscotch, the reality is the old stones are stained by decades of grime and filth.

 

[cotedupy]

Not that it proves anything either way, but once you crack into them, the butterscotch layer is actually a pretty thin skin.

View attachment 1673750

That certainly is quite thin isn't it, and would actually I think be concurrent with either; lightstrike, oil penetration, or just general oxidation of something else in the stone.

Still got that chunk? Try wanging it under yer hole in the ozone layer for a month or two and see what happens. My hunch is that the colour is more likely to be a 'tanning' effect from UV, than from dirt or oil. There's not much that ultraviolet radiation won't have a crack at messing with in some way...

 

[Legion]

That certainly is quite thin isn't it, and would actually I think be concurrent with either; lightstrike, oil penetration, or just general oxidation of something else in the stone.

Still got that chunk? Try wanging it under yer hole in the ozone layer for a month or two and see what happens. My hunch is that the colour is more likely to be a 'tanning' effect from UV, than from dirt or oil. There's not much that ultraviolet radiation won't have a crack at messing with in some way...

Yar, that pic was from today. I suppose I could chuck a coin on it when summer comes. And I might. But I bet I’d get more butterscotch effect smearing half of it with oily filth and letting it soak.

 

[cotedupy]

Yar, that pic was from today. I suppose I could chuck a coin on it when summer comes. And I might. But I bet I’d get more butterscotch effect smearing half of it with oily filth and letting it soak.

Do it! If it doesn't work I can just blame the miserable Victorian weather.

 

[Gamma]

That's a good point I'd not thought of before. Rather than oil put on the stone turning it yellow, BLO, or other chemicals in the wooden box might certainly do that over years. Like oak barrels turning whisky brown.

This, actually, is what started me off on the subject... I had a mounted Norton Trans Ark, maybe 1940s, heavily used but the top was basically clean except for some worked-in grunge streaks. . Stone had a crack. I heated the box and pulled the stone and the bottom of the stone 'below the waterline', so to speak, was massively discolored, very yellow. There was a prefect line all around that followed the edge of the bottom of the box. I was never sure if it was from the box, or oil running over the sides and building up in that crevice. but under the glue holding it in place, the stone was not discolored. Pretty sure it was the oil though. I also had a Norton Trans Ark in cardboard, but with the inner wrapper still in place. Someone put the stone back in the box, wrapper and all, with oil on it. One corner of that stone was yellow as hell, and the shape of the yellow matched the pattern on oil soaked wrapper. Like a fingerprint. The discolored corner of the stone was definitely, at least mostly, caused by oil in that case.

But also feasible that finished wood boxes, or even printed cardboard boxes, could also affect the stone.

When we grind on these stones, or any stones actually, the swarf embeds and discolors the stone's working surface until it is cleared off. Yellow oil permeating the stone is the same thing, just more global across the top since the oil spreads across the surface where working-caused swarf build up is usually more localized. Silica transmits light well (translucent) so only microscopic ingress is needed to create a hue over a larger area. Fiber optic cables are, essentially, made from silica, so the transmission level can be very high in a very pure stone. But when we lap the stones, the swarf or oil is removed or minimized - maybe cleared 100%, and the stone is new-looking again. Pretty standard stuff. But I also think there is more than one thing adding to the storyline...

A translucent Ark that was wiped clean with soap and water can still leave an oil stain on paper if it's left to sit for a while. Had a 4x2x1 Norton Trans in SG for a month that left an oil stain on white cardboard a few months later. So there is enough permeability in the surface of these stones to allow a liquid to ingress and the creep back out again.

 

[H Brad Boonshaft]

I have bleached butterscotch translucents and Lilly Whites, white by soaking in Simple Green and Awesome for well over a year, changing the solution every few weeks.

They release oil slowly but do come back to white. I suspect it is oil that penetrated the stone, when I changed the solution it had a layer of oil on the top.

I don’t think many stones sit out in the sun much. I do store my daily drivers on a wall, on plate racks, but not in direct sunlight.