So I was thinking of necromantic schtuff, which meant it must be a day that ends in a 'y,' and I realized that Coldweave would be nifty to include as a specifically necromantic magical item (or alchemical treatment).

This version wouldn't involve the maidenhair plant (which was clever, and I'd keep), but instead involve the hair of a deceased person, woven and treated to trap residual necromantic energies lingering within the tissue, energies which would suck in light, warmth and even (to a very limited extent) life around them.

This 'darkweave' would become darker than it was in life, as it draws light into itself, and would always feel cool to the touch, and somehow *sharp* even though it was simple woven fibers of human hair. The feeling of it being rough or sharp would be a side-effect of its necromantically charged nature, and the cloth itself would be uncomfortable against bare skin (no game effect, just uncomfortable), being more prone to chafing and promoting sores, so that it would be worn with something underneath it, a bit of underclothing to protect living skin from its necromantic 'hunger.'

One unsettling side-effect of this is that necromantic darkweave is very slightly vampiric, so that blood landing upon it leaves no stain and is absorbed into the fibers.

A person wearing a full suit of darkweave finds that he recovers one less hit point / day, as the suit draws warmth and life from him. Extensive darkweave wearers often have paler than normal skin, as even a partial suit of darkweave tends to absorb light before it reaches the skin. Different wearers seem to react differently to the life-draining nature of the suit, some reacting more extremely to pain, others 'getting used to it' and becoming almost innured. (Again, in game effect, just 'color.')

One societal side-effect of darkweave is that residents of Hollowfaust are encouraged to mimic the long flowing hairstyles displayed by the ruling necromancers (who also occasionally sport long flowing beards as well). This is a matter of convenience, so that more hair will be available on the decedents for use in manufacturing this special necromantically charged cloth. (This is an echo of the development in Thay, but in this case, the upper class spellcasters have no way to mandate their desire for their 'herd' to grow long hair, other than to grow magnificent manes themselves, and hope that the lower classes emulate them.)

Maidenhair fibers might be a later development, safer and easier to harvest (and on the wearer) than the old necromantic version, and the maidenhair vine might specifically grow in still-warm volcanic ash, drawing sustenance as much the heat of their surroundings as another plant would from the sunlight.

Perhaps the maidenhair plant has been tainted by elemental or even fiendish influences, perhaps its heat-absorbing properties, preserved by alchemical processes when made into clothing, are 'natural,' much like those of thermophilic bacteria in the deep ocean. In either case, when the settlers would have arrived, the maidenhair vine crept in patches to the very brim of the caldera, sometimes crawling so near active sources of magma that it was charred and destroyed, like a moth attracted to flame. This version of maidenhair might be very distantly relate to Brown Mold, although without any supernatural abilities relating to cold or fire, simply a tendency to thrive on heat and feel cool to the touch in any environment. Mists would be common around maidenhair plants, a further example of how the plants thermophilic nature aids it, as it helps to attract water to condense on the leaves, in an otherwise arid environment.