Before we dive into the lore of the Bluecaps, here's a short excerpt from my historical fantasy series featuring my version of these mine-dwelling fae in book two - The Verderer.
Silas sat up, wiping at a tear that had pressed its way free as he grew accustomed to the return of light. There at his side stood a startling creature. She looked as though she’d been carved from the same crystal that pervaded the chamber. She regarded him through opaque eyes, their shape reminiscent of a perfect tear; her lips fuller still than Pitch’s, her hair a crystalline imitation of dead straight strands that hung down to boyishly narrow hips. Striking as she was, Silas knew not where to place his own gaze. Her pert breasts, smoothed of all sign of nipples, rested almost directly in his line of sight. He dropped his gaze. But he’d not hide from embarrassment there, for she was entirely naked. His only saving grace was that she appeared as though a statue had come to life, one smoothed of the crevices and folds that were normally to be found between a woman’s legs. - Excerpt from The Verderer - Pitch & Silas Book Two
This is a read-in-order series—Check out Book One with this link.
Bluecaps in Folklore
My version of these underground dwellers leans into the seductive, ethereal nature of the fae in vaguely human form, but folklore describes the bluecaps as having no defined or humanoid features at all, but rather as a blue flame.
This blue flame is said to lead miners to rich ore veins, or warn them of impending cave-ins. The bluecaps are particularly helpful fae, too. They are known to chip in with the work, and their flames could be seen above the heavy mine carts, pushing them along the underground rails.
The bluecaps don't work for free though. They expect a decent payment for their work, and will let their displeasure be known if they fell they were undpaid, but on the flipside, are strikingly honest, and silver will be returned if they believe they have been paid too much for the work they've done. They don't work on Saturdays, or on Christian holidays, because evidently they are respectful fae, too.
There are many different types of 'mine spirits' in English folklore, often dependant on the area of the country where the mines are found. Bluecaps are border-land creatures, found in the Yorkshire lead mines and elsewhere along the border between Scotland and England. In Yorkshire they were called the 'ghost shift' on account of their working only late at night; their hammers being heard far down in the mines, chipping away at the precious ore-rich seams.
Science can suggest several origins of the bluecap myth. Firstly, a mixture of gases, in particular methane, will produce a small blue-ish flame when it meets an exposed flame - like that which came from a miner's candle. (So long as the amount of methane is small enough to avoid a huge explosion!)
Another theory is that glowing funghi inspired the tales, or sulfur and trace minerals in the rock that can produce small flames.
Though we may never now what inspired these stories, it's easy to understand why. The mines were dark oppressive and dangerous places. Places where fire turned blue, and mysterious sounds came from depths of mine shafts. Places where imaginations of the miners, tired after long endless days of work, would run wild.
In my series, The Diabolus Chronicles, the bluecaps live deep below the mines, in a world of blue quartz rather than blue flame, but they are as helpful as the lore describes.....almost. Their idea of what is helpful has become dangerously twisted, and those that enter the mines now do so at their own peril. 