Author Topic: Picture of the Day  (Read 229650 times)

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Offline Oblomov

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Re: Picture of the Day
« Reply #2760 on: December 29, 2016, 12:40:27 AM »
Weardale fluorite, possibly the best piece discovered, found in 1818.



Exceptional.

I always heard a lot about Bluejohn, coming up to Sheff and Derbyshire. Never really saw why people raved about it. Then I discovered how its made. A large chunk of it is simply acrylic resin.

Would the fluroite luminesce in the presence of cathode rays?

Offline Tony

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Re: Picture of the Day
« Reply #2761 on: January 15, 2017, 10:39:38 AM »
Acrylic resin is a new one on me but surely that's some kind of trading standards issue, assuming that somebody would care.
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Offline Gormenghast

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Re: Picture of the Day
« Reply #2762 on: January 15, 2017, 12:36:16 PM »
It's very fragile. They use resin to hold it together, otherwise it would shatter when being worked.

Offline Alastair

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Re: Picture of the Day
« Reply #2763 on: January 15, 2017, 07:57:08 PM »
Exceptional.

I always heard a lot about Bluejohn, coming up to Sheff and Derbyshire. Never really saw why people raved about it. Then I discovered how its made. A large chunk of it is simply acrylic resin.

Would the fluroite luminesce in the presence of cathode rays?


I never heard about Blue John being held together by acyrylic resin. What about the antique pieces that predate acrylic resin like these? - https://www.fellows.co.uk/blog/antiques/2015/10/13/auction-report-the-blue-john-sale/

I'm sure fluorite would fluoresce under cathode rays, aster all it's what fluorescence is named after. It glows even in daylight just from the UV from the sun. That piece of purple/green classic Weardale fluorite is in fact green, with the blues and purples coming from natural fluorescence in daylight. It would look just green under a tungsten lightbulb.

Here's another recently mined piece which has the natural fluorescence. It's from the Rogerly Mine which has been reopened by a group of American enthusiasts as a commercial venture to supply collector specimens since the good stuff sells for a lot of money -




Offline Tony

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Re: Picture of the Day
« Reply #2764 on: January 17, 2017, 06:15:01 PM »
Why's it called Blue John? Who's John?
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Offline Alastair

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Re: Picture of the Day
« Reply #2765 on: January 17, 2017, 09:38:38 PM »
Why's it called Blue John? Who's John?

The theory I've heard is it was called Bleu Jaune, French for blue yellow because of the blue and yellow banding.

It seems a bit unlikely, because why would it have a French name?  Also the bands are hardly yellow.

Offline Oblomov

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Re: Picture of the Day
« Reply #2766 on: January 18, 2017, 12:51:44 AM »
Pine resin was used before epoxy became the stabiliser of choice -
via wikipedia:
Before they can be worked, the stones (having been air-dried for at least a year) are heated in an oven, then placed in a bowl of hot epoxy resin (previously, pine resin was used), and then further heated in a vacuum oven. This drives out air from minute pores in the stone, and replaces it with the resin, which binds the otherwise friable crystal structure, allowing it to be cut and polished. After resining, the stones are cut on a circular saw. They may be made into rough cuboids or cylinders ("rough-outs"), for turning as bowls and vases, or flat slices, for making jewellery.

I originally found out about the resin from Treak Cliff Cavern tour (my 3rd).

I really don't see the attraction in it - but that might be the ghastly stuff it was made into.

Offline Alastair

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Re: Picture of the Day
« Reply #2767 on: January 18, 2017, 04:39:31 PM »
No I don't see the attraction of most Blue John either. I see it made into jewellery in the gift shops of Castleton and it's totally unsuitable to be worn as jewellery because it's far too soft. Gemstones need to be hard so they don't scratch. Fluorite has a hardness of 4 on Moh's scale which goes from 1 to 10 with diamond being the hardest at 10. Gemstones start at a hardness of 7.

Blue John is kind of interesting geologically because no one is quite sure how it got its colour. One theory is it is from local radioactivity as Castleton is a bit of a hot spot. The other theory is that it got it's colour from local hydrocarbons.

There's elaterite, a kind of radioctive tar that seeps out of the limestone at Windy Knoll and also bitumen - or there used to be. I've never found any and I've been up there with my Geiger counter to try and find some.

http://www.mindat.org/loc-5012.html

“The abundance and variety of residual oil shows in the Castleton area suggest that, before the removal of the Namurian cover, the shelf margin crest and the northwards inclined shelf margin succession could have hosted a significant oil accumulation. The elaterite of Windy Knoll to the west of Castleton provides the best exposure of a residual oil body. Windy Knoll forms a small culmination on the ridge crest that was previously completely top and side sealed by the Edale Shale Formation. Our field work suggests that the base of the elaterite defines a residual oil-water contact (OWC). Bitumen impregnation in limestone breccias below the OWC may indicate the charge pathway. These breccias were found by Peacock & Taylor (1966) to be radioactive. If the bitumen and uranium are genetically associated, an indication of the area formerly open to oil migration is provided by Peacock & Taylor’s map of surface uranium anomalies. Radioactive anomalies occupy the entire 6000 m long, 500 m wide and 150 m high exposed portion of the slope to the south of the anomalies persist in depth. They illustrate samples of bituminous calcite and uraniferous phosphatic limestone collected from caves in the Castleton area.” (Cameron and Ziegler, 1997, p. 138 ).

Offline Alastair

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Re: Picture of the Day
« Reply #2768 on: January 19, 2017, 11:44:55 PM »
Possibly the worst Blue John artefact ever.

For sale at Sheffield Auction Gallery at the end of the month.

https://www.the-saleroom.com/en-gb/auction-catalogues/sheffield-auction-gallery/catalogue-id-srsh10147/lot-977893a9-fb3b-4960-98cc-a70000e44c9f


Offline Oblomov

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Re: Picture of the Day
« Reply #2769 on: January 22, 2017, 12:14:26 AM »
That's so thoughtless and casual.

This is the sort of stuff that has me on the verge of regurgitating:


Offline Alastair

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Re: Picture of the Day
« Reply #2770 on: January 23, 2017, 12:57:43 AM »
They might not be to your taste or mine, but there's huge skill and craftsmanship in those pieces that can be admired.

Unlike that ****e lamp stand.

Offline Alastair

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Re: Picture of the Day
« Reply #2771 on: February 20, 2017, 01:52:59 AM »

Offline Alastair

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Re: Picture of the Day
« Reply #2772 on: March 16, 2017, 05:56:02 PM »
I think they mean break down, but pretty accurate -


Offline muddycoffee

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Re: Picture of the Day
« Reply #2773 on: February 11, 2018, 05:31:26 PM »
I am really pleased a couple of weeks ago to get this far with creating code to interpret and display results from my rain gauge.

The first one is a bar graph of the rain volumes for the current day and the previous 14 days.


The Second is a graph showing today's rain activity.


The rain gauge is connected to an Arduino which counts the tips and a Raspberry Pi collates the data, processes it and draws the graphs using Matplotlib. It also hosts a database of historic weather data and publishes it on a webserver.

Offline Oblomov

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Re: Picture of the Day
« Reply #2774 on: February 18, 2018, 08:26:25 PM »
Tidy!