I've come up with what (I hope) is an interesting and useful new spell and could use some opinions on it.
Dread Etching: Cr(Re) Aq 5
R: Voice, D: Conc, T: Ind
Creates a small amount of acid dealing +1 damage that the magus can control and move by concentration. This has minimal combat applications; those in a fight would do better to employ The Alchemist's Revenge (HoH: S 35). However, it has a variety of other applications such as exploration, art, and subtlety. In particular, the Concentration duration ensures that should the magus be distracted, the acid disappears and cannot be used against him.
+2 Voice, +1 Conc, +1 Rego Requisite
-Lucius ex Jerbiton uses this spell to help him sculpt a statue out of a block of stone. Being deficient in Terram magics, he finds this spell helps augment his craft ability. As the spell takes place over time and is intended to supplement his Craft roll, the Finesse roll to help him shape the statue is easier than it would be for instantaneous Rego Craft Magic.
-Alana ex Flambeau, a respected hoplite, is rumored to have used this spell to encourage an Infernalist to provide information. She also used it to unhorse several riders by making their mounts panic.
-Armand ex Verditius uses careful applciations to etch his trademark into all blades he smiths in his Toledo shop.
-Marance ex Tremere finds this highly applicable for gaining access where needed: He has used this to pick a lock, create a new window, and dissolve a dangerous magic circle.
It certainly sound like you've put a lot of thought into the uses for it. A very useful spell indeed.
However, as for sculpting with it I think maybe that's too good. believe me, I've thought about designing Re(Pe)Te spells to aid the mundane sculpting abilities. but to my knowledge there are no magical guidelines and rules to support this. HpH:Soc in Jerbiton chapter mantions Creo magics and Rego Craft Magic. If anything, it would require several magnitudes for delicate movements and a hefty Finesse roll to be in par with RAW.
But I really think there is something missing, between creating instantly from nothing/crafting from raw materials in an instant and then using completely mundane means. Like if a magus uses ReTe (or Pe) to gently chip away at a rock until he has sculpted a figure (most likely using Finesse), in real-time so it takes the same time as mundane Sculpting ability.
Also, the spell as you mention could be used to etch a message of warning into the forhead of comeone who crosses you.
The example to take about Art comes from A&A, and the rego Craft magic is magically inmediate, but highly difficult to some things with the Finness roll (+9 or +12 many times). This spell should be easy but not the way to crave things, i think that my rule to the craft things should be - Finness +9, you add the half of your Finness Score to the Craft total. After of that, the offensiver effects are likely to be easy to use.
However it does have a application in sculpting that would not require such high Finesse rolls. It could be used to remove large portions of stone with a fairly low roll. Not to mention, the spell could be designed to additionally just add a bonus to the crafting roll or a reduction in time based on success of Finesse roll say diff +6. It would represent broad application of the spell over large portions of the art, but then the creator would need to do fine work manually.
I'm not sure about large amounts of stone- this appears to be a small amount of weak acid, so unless you have a very base type stone... it seems to me that just about anything you do with this spell will require a lot of time and finesse, but aside from that it is a very broad utility spell...
. I do appreciate the feedback though!