|Image of Paracelsus.|
Theophrastus von Hohenheim, "Paracelsus" was the son of a German physician living in Switzerland. He took a degree in medicine from the university at Ferrara and proceeded to wander through Germany, France, Spain, Hungary, the Netherlands, Denmark, Sweden, Poland and Russia. He died in 1541, nearly half a century before the various pamphlets he wrote started to be noticed and reprinted. In his lifetime he was hounded out of one European city after another for defying traditionally accepted medical practices and insisting on doing things his own way. He was known for somewhat difficult personality, and the somewhat gloomy but steadfast conviction that the world would shortly come to an end. Today he is celebrated for basing his diagnoses on a careful observation of nature, and of his patients actual symptoms, a sometimes radical departure from the norm for his time.
By the end of the sixteenth century, his writings were being circulated among the intelligentsia of the Florentine royal court in Italy. His opinions extended not only to medicine and anatomy, but also to alchemy, botany, pharmacology, astrology, and what would later be called psychology. Paracelsus' philosophy was a powerful influence on the education of Antonio Neri in the discipline of alchemy. Neri's father was the royal physician to Florentine Grand Duke Ferdinando de' Medici, and almost certainly did not subscribe to Paracelsan ideas, but Antonio seems to have taken a different path. His benefactor, Prince Don Antonio de' Medici was a confirmed Paracelsan.
By the time Neri's book on glassmaking appeared in 1612, the priest counted himself a devoted Paracelsan spagyricist and he as much as says so. In his introduction, he holds out the future possibility of publishing “the experience of my endeavors over many years, working in diverse parts of the world […in] the chemical and spagyric arts.”  Paracelsus had pioneered two new disciplines that he named "iatrochemistry" and "spagyrics." Iatrochemistry dealt with the use of minerals and chemicals in medicine; spagyrics made use of plants and their extracts. Here we get a hint that Neri's true passions lie beyond the formulation of glass. Speaking about the potential of chemistry in medicines, also in the introduction, he writes, "These are matters of nature to which I believe there is no higher calling in the service of humanity." The same techniques and terminology used to produce medical remedies shows up in Neri's glass formulations. Twice, he refers to ingredients as "medicine,"  which he adds to the glass melt in "doses." He also uses the somewhat specialized apothecary's term 'ana',  which means "in equal parts."
Paracelsus coined the word "spagyric" in his book Liber Paragranum,  where he argues medicine should be based on the physical laws of nature alone. The word derives from two Greek terms: spao meaning to separate and ageiro meaning to combine. The underlying philosophy recurs throughout the history of alchemy. To enhance the special properties of a plant, break it down, to its separate constituents, then purify each and recombine them for a more potent product. Herein lay the bones of Neri’s empirical methodology with glass; one built on the processes of reduction, purification and recombination. These methods appear throughout his technical recipes. Neri utilizes the method with both plant and mineral ingredients, in the preparation of basic materials and pigments and throughout his medicinal work. You could say that these very techniques and the resultant near mania he developed for purification are responsible for the high reputation of his glass formulas. His colors were bright and clear beyond what was produced by typical preparation by artisans of his time.
In letters from his friend Emmanuel Ximenes, around 1600 the two men discuss Paracelsus in their correspondence, but do so carefully since it is still a rather controversial topic.  By 1608, Neri seems a bit more relaxed, writing to a friend that he had cured diseases using the "grandissima meraviglia" (wonderfully grand) methods of Paracelsus. 
Mere months before his own death in 1614, Neri wrote a small tract titled Discorso. The full title translates to 'Discourse on Chemistry, what it is, and its Operations'.  In it, he "manifests right from the outset his adherence to the Paracelsan doctrine, which is not restricted to inorganic chemical operations involving the transmutation of metals, but has broader applicability to the field of medicine."  Neri begins:
The operations belonging to chemistry do not only, as some estimate, involve the transmutation of metals. It is a much more universal art, which in some ways also embraces medicine (or at least it comes very close in assisting) and it can be defined. It is an art, which resolves and reduces all ‘mixed bodies’ [corpi misti] into their primary elements, it searches out their nature and separates the pure from the impure and it makes use of the pure to perfect these bodies and even to transform one body into another. History has mostly remembered Neri as a glassmaker, but his own philosophy was a bit different. He considered himself first and foremost an alchemist and his art—the art of chemistry—was a discipline that embraced metallurgy, glassmaking and medicine.
 often referred to as Philippus Aureolus Theophrastus Bombastus von Hohenheim, this concatination was not used to refer to himself. for a fascinating discussion see Thony Cristie's post here: https://thonyc.wordpress.com/2012/05/01/whats-in-a-name-2/
 Neri 1612, p. vii.
 Neri 1612, pp. 40, 104, medicina; p. 9, dose and throughout.
 Neri 1612, p. 98 ana
Opus Paragranum, written in 1529/30 not published until 1565. Cf. Paracelsus 1565.
 Neri 1980, pp. xlii–xliii, lix. In his letters, Ximenes is careful about references to Paracelsus.
 Neri 1608; Zecchin 1987–89, p. 157. “… che già stava in casa il s.r. Zanobi Bartolini, che mostra gl’ effetti di mali da lui guariti secondo gli ordini Paracelsici di grandissima meraviglia…” [that previously when in the house s.r. Zanobi Bartolini showed the effects on sicknesses that he healed using the instructions of the great and marvelous Paracelsus ....].
 Discorso sopra la Chimica, che cosa sia, e sue Operazioni, Neri 1613.
 Grazzini 1983, p. 221.
 For the original Italian, see Grazzini 2012.