Blue John Mine & Workshop Techniques
Occurring in small deposits which line the walls of the caverns or fill the cavities of the pipe veins, the availability of Blue John for modern day craftsmen has been greatly impacted by the carefree excavation of previous generations. Today, out of the three most prolific mines – Blue John Cavern, Old Tor Mine and Treak Cliff Cavern it is only Treak Cliff which mines any gemstone quality material. Unfortunately, the opportunity to craft such grand statement pieces is simply not possible as the mine production is now restricted by the volume it can extract and more significantly, by the size of the individual pieces of material that can be found. The deposits of quality stones are found in veins of about 3 inches in thickness or in nodular form and most commonly extracted in fist-sized pieces or smaller. Rare finds are still made up to 50 kilos, but their gemstone quality would be questionable and often sorted for geological specimens and research.
Although mining is a delicate process, fundamentally the working of Blue John has not greatly changed through the past two hundred years. The techniques are still the same, the only difference is the form of power used to operate the lathes and wheels, whilst the old implements have been replaced by modern-day tools. With the afore mentioned restrictions in mining, it is reflected in the type of Blue John product we see crafted today. Although we do see limited manufacture of vases, bowls and other ‘large’ articles, a more dedicated industry devoted to the design and production of award-winning fine jewellery is allowing Blue John to thrive in the 21st century.
Due to the fragile nature of the stone (rated 4 on the Mohs scale) it has to be initially extracted with great care to avoid any damage – which usually involves the removal of any surrounding limestone. With various mining methods being used throughout the years, the process of drilling and wedging – also known as ‘plug and feather’ – is one that has been commonly used and involves drilling into the limestone alongside the Blue John. Although heavy duty electric drills have replaced long drill bits which would have been turned by hand in the old days to make the holes, the use of metal wedges hammered into the wooden plugs - which are placed into the holes - causing the limestone to split are of a similar nature. Once split, the limestone will come away from the walls and pieces of Blue John can be removed. In today’s modern environment a stone cutting diamond tipped chainsaw is used. Causing less vibration and noise, it also allows less damage to the stone with the benefit of more regularly shaped and larger blocks being cut out in a single piece.
Once extracted, the stone is left to dry naturally and takes up to 18 months to do so. At this stage the Blue John would be impossible to cut and is subjected to a strict heating and bonding process, the first stage of which is to warm the Blue John in an oven. Once heated to a satisfactory level, it is then submersed into a 50/50 mix of resin and hardener and then placed in a vacuum oven which allows the liquid mix to slowly penetrate inside of the internal structure of the stone. A period of time is then given for the Blue John to drain off its excess covering, before it is returned to the oven and ‘baked’ for a final hardening of the stone. In a modern-day workshop environment, it takes around 3 days for the Blue John to become workable.
Having reached the cutting stage, the workshop craftsmen will cut the hardened Blue John into slices with specific uses in mind. Whether working on a ring, pendant or brooch with the use of a lightbox and a trained eye each piece is selected for its particular setting. A process of shaping and gradually offering the stone to fit the setting is then undertaken with the use of a small jewellery grindstone. For the stones/designs which are flat underneath it has been common to paint the underside white, so to increase reflectivity.
In 2010 C W Sellors moved this process on a stage and patented the use of Mother of Pearl to back the Blue John gemstone which not only offers a light backing but wonderfully radiates the finished piece.