The second in Legendary Games' Gothic Grimoires-series is 8 pages long, 1 page front cover, 1 page editorial/SRD, 1 page how-to-use, 1 page back cover, leaving us with 4 pages of content, so let's take a look, shall we?
We get a grimoire...that is blank. No, really. The Inverse Calculus of Unseen Refraction is a tome with an attached crystal lense, which, even when applied, lets you read nothing on its blank pages - for the book was written with ink laced with phantom fungus spores, remaining invisible. Only with a respective spell can the hidden meanings be unearthed. As all grimoires, this one can substitute access to certain spells when crafting and provides additional bonuses to its students as well as coming with an interesting background story. Beyond these, the tome also contains new special feats and rules, first of which would be the metamagic feat Unseen Spell: At +2 levels, these spells make avoiding them harder, even mitigating e.g. improved evasion down to evasion and the like. Also, alchemical extracts can similarly be enhanced, at only +1 level.
Speaking of alchemy: The tome also contains 6 new discoveries that allow alchemists to create items in powdered instead of liquid form, allowing them to mask them in a variety of different items. They may also use their own level to determine efficiency of invisibility spell, make their bombs invisible, protect versus divination when invisible, modify invisibility to last for a bit even after being dispelled and even create a mutagen that makes for invisible for its lengthy duration to go full-blown invisible man.
Alchemists also get access to 8 new spells/extract-formulae herein: From an alchemist's level 6 mind blank, a sphere that renders invisible creatures visible, but still grants them 20% concealment (usable offensively and defensively), condense willing creatures or objects into a liquid (which you can carry around and then recreate - glorious plot-spell and useful for infiltrations), a combination of invisibility and blur (which might attract hounds of Tindalos - beware!) and a very cool idea: You can now create a well of invisibility that turns every creature that passes through its square invisible - the nasty double-team actions with alchemists, rogues and vanishing spellcaster should be apparent immediately and at least on me, they had the result of me chuckling at the maleficent possibilities this spell has. "Not there" is a means of phasing in and out of visibility and making yourself or allies transparent (again, with a cost...) also ranks among the most iconic, interesting options I've seen in a while. Finally, you may glitterdust/petrify foes, turning them to fragile glass - shards are supposed to be lucky, but your players may disagree...
Editing and formatting are top-notch, I saw no glitches. No wonder, mind you - they probably are invisible. ;) Layout adheres to legendary Games' drop-dead-gorgeous 2-column full-color standard with a glorious artwork for the grimoire of the quality that makes these pdfs such a joy to look at. The pdf, in spite of its short size, comes fully bookmarked, which is awesome indeed and makes navigation even simpler. The pdf also comes in two versions, one being printer-friendly.
Legendary Games continue their trend of high-class, premium-content, stellar supplements and continue to provide brilliant grimoires as per their innovative concept as originally outlined in their "Tomes of Ancient Knowledge" and "Meditations of the Imperial Mystics"-pdfs. After bards got their due in "Necrotic Verses", alchemists now get a supplement that ranks, even if you just mine the content sans the grimoire (but why would you?) among the best supplements ever released for the alchemist, dripping flair, style and tactical options. Before I'm starting to sound like a broken record of heaping praises and superlatives, I'll conclude this review with the words that this grimoire is worth every cent f the very fair asking-price and thus clocks in at 5 stars + seal of approval.