Books of Secrets (also called Secreta) are a whole genre of books I didn’t even know existed a little while ago. Genres (I mean like the novel, the epic poem, the Christian hagiography) are like media: they peak, and then they convalesce, and sometimes they die. The book of secrets is an example of a dead literary genre… sort of, though the conceptual basis and the ideology are alive in well, in transmuted form.
In their original form, one might look at them basically as recipe/how-to books–and it was through the translation and distribution of books of secrets that alchemical knowledge proliferated in Western Europe, with notable changes to industry: they had lots of recipes for things like glue, cosmetics, medicinal ales, and so on. One example is the text A Booke of Secrets: Shewing diues waies to make and prepare all sorts of Inke, and Colours, which was published in English translation (from the Dutch) in 1596, and which also contained a fair bit of technical (for the time) information on the fermenting and preservation of wines. (A PDF of the original text is available here.)
Other, similar books contained other “alchemical” information, including technical explanations of distillation… which is one of the ways that the industry of distillation exploded in the 1600s in Continental Europe.
William Eamon argues that there’s a lot more to them than just recipes, in his chapter on the subject, “How to Read a Book of Secrets” from Secrets and Knowledge in Medicine and Science: 1500-1800 (ed. Elaine Leong and Alisha Rankin, book link here).
What more? Well, he argues that there are multiple ways of reading a Book of Secrets, but that most importantly, they represent important changes in the distribution and presentation of specialized knowledge in European civilization, among other things. So, think of them as a kind of Renaissance-to-industrial-revolution alchemical/culinary/scientific/medicinal equivalent of Instructables.com, distributed the way the Anarchist Cookbook was.
Which is to say, they were useful to those in the 1500-1800s who partook of a sentiment vaguely like that expressed by Bruce Sterling in the first statement of Viridian Principles:
The boundaries that separate art, science, medicine, literature, computation, engineering, and design and craft generally are not divinely ordained. The most galling of these boundaries are socially generated entities meant to protect the power-interests of knowledge guilds. This is not to say that that all research techniques are identical, or that their results are all equally valid under all circumstances: quantum physics isn’t opera. But there exists a sensibility that can serenely ignore intellectual turf war, and comprehend both physics and opera. You won’t be able to swing a grant or sing an aria by knocking politely at the stage door. They won’t seat you at the head of the table and slaughter the fatted calf. But you can take photographs, plant listening devices and leave. If you choose, you can step outside the boundaries history makes for you. You can walk through walls.
In the 1500s, you didn’t plant listening devices or take photographs, you wrote and translated Books of Secrets. And that’s how you get a Renaissance going (and keep it going, too).