Oldblood

Oldblood, also known as Heartsblood, was a type of purple dye produced from the secretions of hunting knight snails.

Price
The price of this dye was typically rather expensive, due to it being rather difficult and time-consuming to gather enough snails for a good batch.

Creation
This dye was produced by exposing the secretions of hunting knight sails to sunlight. Several species across the seas of Toril could be used for this purpose.

Typically large numbers of hunting knight snails were gathered and crushed in order to form a batch of this dye, but as population numbers declined due to overhunting people would resort to instead keeping the snails alive and milking them. This took a lot of work and was usually done by young or aging members of fisherfolk families.

Background
Ed Greenwood noted that this dye was the Realmsian equivalent of Tyrian purple.