If this has been done before please let me know, no need to reinvent the wheel.
The main idea is the result of an encounter where my Muto and Rego specialised Tremere wanted to walk across water to get to someone.
It got me thinking and what I came up with was the following.
Starting with the Rego Aquam guideline to turn a liquid into a solid (I forget the base, it's not terribly important for the theoretical discussion fo the spell though).
Or, use MuAq(He) to turn water into wood.
Range = touch +1 magnitude (I want the water to turn to ice/wood under my feet as I walk)
Duration = diam +1 magnitude (could be Sun if I wanted for anothe rmagnitude)
Target = part +1 magnitude (I'm not turning the whole lake to ice, just the area beneath me)
Please ignore (for now) any issues about keeping balance on the ice or not slipping, we can address those later.
I want to step onto water and when my foot hits the water it creates ice beneath it to support my weight, as I walk I turn more of the water to ice where I step. Ideally, as I walk the ice melts back into water.
This got me to thinking, how does a Touch range Diam Duration spell work? does it:
a) turn an amount of water that I can touch a part of defined by the target to ice upon casting and then keep it as ice for the next 2 mins?
b) create an effect that lasts for the next 2 mins that causes any water I touch to turn to Ice?
For my spell to work as intended b) would have to be a valid interpretation, is it?
Then I run into a problem of volume, the base individual for Aquam is a pool of water 5 paces across and up to 2 paces deep at the centre. using interpretation a) above that is how much of the lake I could turn to ice if the spell just turned an "individual" sized part of the lake to ice upon casting. If b) is a valid interpretation of the spell guidelines what happens as I walk across the lake and the path below me freezes and the total volume of water I have frozen reaches 1 "Individual"? does the spell stop freezing water? does it matter if I have the water unfreeze as I walk away from it so that only 1 "individual" sized piece of the lake is frozen at any one time, like a disc under me?
If none of that will work, could I have it target "self" and work similar to a "ward against rain" that rather than pushes water away from me and keeping me dry freezes water that contacts me?
Any thoughts? I thought it would be a cool idea to cross water and I just want to make sure it makes sense within the hermetic guidelines.