The so-called 'Tanglefoot Bag,' also known as the Spider's Purse and the Alchemical
Gluepot.
There is really only one efficient method to create these concoctions, and
I use a much less efficient method, because I personally loathe spiders, even
the tiny mundane ones that spin cobwebs in the corner, while the monstrous dog-sized
creatures that are typically kept in captivity and 'milked' by professional
alchemists for the sticky webbing necessary to craft a tanglefoot bag make my
blood run cold, with their cold, alien eyes and their far-too-many twitching
legs.
Still, this is the accepted practice, to capture a monstrous spider the size
of a small dog, or perhaps slightly larger, and to keep it in a bamboo cage,
with many bamboo rods stored nearby. When it is 'milking time,' the bamboo rods
are inserted at one edge of the cage, slowly forcing the hissing agitated creature
back against one wall, and then being inserted very carefully (so as not to
damage the loathsome abomination) to restrain each of it's legs. Then a section
of the cage near it's backside is unlatched, leaving it's arse hanging out of
the cage. Some unluckly apprentice gets the job of stroking it's underside with
a brush of horsehair, while another spins a ceramic rod just under it's spinnarets,
slowly rolling up the silk that it instinctly produces in response to the stimulation
of the brush. This process takes over an hour, and many ceramic rods are handed
off, coated in thick wads of the silk, like spun sugar candy at a festival.
If the rod is spun too fast, the spider stops spinning and the process must
often be started again, as the creature is generally quite unhappy with the
entire process, although it enters a contented state while it is slowly spinning
it's web, despite the situation, almost as if it is in a trance of some sort.
If the rod is spun too slowly, strands of silk drape to the floor, get stuck,
get dirty, and it's all a terrible mess and someone is going to get stuck on
abdomen-tickling duty, next time.
Between 'milkings,' the repulsive creatures are fed pigeons or rats, neatly tied up (so that they won't accidentally damage the precious monsters), and that's yet another thing I won't have done in my laboratory.
Instead, I use a resin derived from trees known as copal (which is not to be
mistaken for mere sap!). Gallons and gallons of this resin must be distilled,
and mixed with white chalk, rendered animal bones and skin, and the gummy mucus
secreted by common garden slugs. It's a terribly painstaking process, and 'milking'
garden slugs, if anything, is a dreadful tedium, but it's a sacrifice I am willing
to make to not have a nightmarish beast from the darkest parts of the abyss
living in my laboratory.
However the substance is made, the substance must be kept warm, and poured into the 'bag' for which is named while still quite hot to the touch. Once it begins to cool, any contact with air will cause it to begin to harden, and a Tanglefoot Bag that has been left open will become useless in quick order, degenerating into a chalky white (in the case of spider silk derived gluepots) or pale yellow (for tree resin derived adhesives) substance that feels somewhat like brick or shale, but crumbles into useless powder at any forceful contact.
Because of this trait, it is easy enough to determine if a Tanglefoot Bag that
has been found or purchased is still 'fresh' and effective, as it will feel
soft and yielding to the touch, while one that has lost it's potency feels like
a rock in a bag (which it essentially is).
Tales of alchemists whose 'dog-sized spiders' turned out to be immature specimens
that grew to the size of a horse, and were fed recalcitrant apprentices to keep
them in silking trim, are surely just tales told by cruel, cruel people to frighten
old men.
Shame on them.