The Twelve Keys of Basil Valentine, first published in 1599, is a significant alchemical work attributed to Basil Valentine. However, historical evidence suggests that Johann Thölde, the publisher, was most likely the true author. The book is structured as a sequence of allegorical narratives accompanied by images, intended to convey alchemical operations and principles related to the creation of the philosopher's stone.

The text is divided into two parts. The initial section discusses general alchemical concepts and provides guidance on the pursuit of the philosopher's stone. The second part, specifically titled 'The Twelve Keys,' comprises twelve brief chapters. Each 'key' offers an allegorical depiction of a stage in the alchemical process, with symbolic names for ingredients changing as they are transformed. The language and imagery are designed to be obscure, requiring a knowledgeable reader to decipher their meaning.

The core of 'The Twelve Keys' lies in its allegorical method. The text uses veiled language and symbolic imagery to describe alchemical procedures, aiming to both conceal and illuminate the processes involved in creating the philosopher's stone. Each of the twelve keys represents a distinct step, with critical ingredients referred to by code names that evolve as the substances themselves are transformed. This approach suggests that the work was intended for an audience with a pre-existing understanding of alchemical symbolism and practices, as only such adepts would be able to correctly interpret the layered meanings within the text and its accompanying visuals.

The initial 1599 publication of 'The Twelve Keys' did not feature illustrations. Visual elements were introduced in the 1602 edition through woodcuts. Later, in Michael Maier's 1618 Latin translation, 'Tripus Aureus' ('Golden Tripod'), revised engravings for all twelve steps were included. As the textual content predates the images, scholars generally consider the original writings to be the primary source of the work's alchemical teachings. The development and addition of visual aids over time reflect the ongoing interest and attempts to clarify the esoteric content of Valentine's work.

Modern analysis, particularly in the 21st century, has explored physicochemical interpretations of the text. Chemists and historians have experimentally investigated potential chemical processes that might correspond to the allegorical steps described. These interpretations suggest that some keys may describe actual laboratory techniques and observed results, while others might represent theoretical extrapolations or ideas based on earlier alchemical writings. The enduring influence of 'The Twelve Keys' is highlighted by its study by prominent figures in scientific history, such as Robert Boyle and Sir Isaac Newton, who are believed to have seriously engaged with its contents.