alchemical poison detection

"You don't need a good taster if you have a good alchemist, but they cost about the same."
-Duke Nanda Frymar

alchemy ultimately boils down to being the science of transformation. One common effect from alchemical reactions is color changing. This is usually used to teach apprentice alchemists basic reactions in a safe way or to entertain children, but eventually an alchemist who was also a doctor and herbalist came up with the idea of using alchemical color changing as a diagnostic tool.
Certain alchemical mixtures change colors in the presence of certain poisons. This has been used by many nobles to protect themselves against food or drink based poisons.
Certain alchemical mixtures change colors in the presence of certain diseases but this is uncommonly used because each disease requires a specific concoction whereas one alchemical concoction can detect many kinds of poisons.
Disease detectors are often used to control specific plagues or to test communal water supplies.
Certain substances can react with blood samples to cause color changes in the presence of certain conditions but at this is mostly used for autopsies rather than in a diagnosis/prevention manner.
With advanced training (and expensive ingredients) alchemists can concoct mixtures that cause color changes when exposed to supernatural curses.

Utility

Normally a sample of the food or drink being tested is separated to it's own container and a drop or pinch of the appropriate alchemical mixture is put in.  If the color changes, the sample is tainted.

Parent Technologies

• alchemy

Inventor(s)

Fragments of surviving ancient writings shows that this science existed at least via elven inventors during the the Second Age but the knowledge was lost during the Second Unmaking.
This process had to be re-invented during the Third Age by a wide variety of alchemists across Scarterra. Each disease, toxin, poison or curse needs a different mixture to detect, so there are many different inventors for many different related applications.

Access & Availability

The lore to use color changing diagnostic alchemical mixtures is wide spread, but the cost is fairly prohibitive (as it is for most alchemical creations), so these substances are mostly used by the upper classes and those who work for them as well as the various priesthoods.

Discovery

A great many alchemical reactions cause color changes.  This was normally viewed as inconsequential byproduct of alchemy until some alchemists theorized that the color change itself could be useful.

Related Species

• elves
• humans