copperases

Noun

copperas (usually uncountable, plural copperases)

1. (historical, usually, inexact) Any of various metallic sulphates formed from the reaction of sulfur with iron, zinc, or copper, especially (alchemy) solutions of such compounds misunderstood as a mediator or catalyst for the transmutation of iron into copper &c.
   • The ſecond way whereby bodies become blacke, is an Atramentous condition or mixture, that is a vitriolate or copperoſe quality conjoyning with a terreſtrious and aſtringent humidity, for ſo is Atramentum ſcriptorium, or writing Inke commonly made, by copperoſe caſt upon decoction or infuſion of...1646, Thomas Browne, Pseudodoxia Epidemica, Book 6, Chapter XII: "A Digression Concerning Blacknesse", p. 336
2. (archaic, usually) Synonym of iron(II) sulfate.
   • It were superfluous to describe the Process of making the Aqua fortis; it shall suffice to let you know, that our common Coperas makes this Aquafortis well enough for our purpose[…]1707, J[ohn] Mortimer, The Whole Art of Husbandry; or, The Way of Managing and Improving of Land. […], London: […] J[ohn] H[umphreys] for H[enry] Mortlock […], and J[onathan] Robinson […], →OCLC

   Synonyms:

   iron(II) sulfate