A buddy of mine is trying to figure out a way to make diamonds so he can easily cast the wish spell once he reaches level 20. He currently says he can use Alter reality to turn gold into onyx powder then onyx powder into a single diamond. Would that in any way work? or is there another way he could just make diamonds?
'free' wish at level 20
..still cost you a spell slot, and you need the gold to turn into onyx and then to diamond.
you can do better if you take the 'true name' arcane discovery and get a name of an efreeti to get your daily 3 wishs out of him.
my 'Shenron mark II' build get by level 20 the following spell like abilities (so no material cost):
any level 0 spell at will, lesser wish 2/day, each of the magic domain,divine subdomain spells 1/day -including resuraction & miracle. and the exalted level 10 class ability perform miracle (which i like to refer to as lesser miracle).
-not including your god's devine boons for exalted, depand on which god you picked.
The diamond itself isn't suppose to limit casting Wish. The cost of the matieral component is suppose to be the true limiting factor. As long as the player is sacrificing 25,000gp per wish everything is fine.
Its when a player wants to find a way to get free/cheap wishes that there is a problem. As a GM you shouldn't allow it. Wish has that outrageous cost because its an outrageous spell. Don't cheapen Wish by lower its material component cost.
Also...if you spend zero gold on a diamond how much is it worth? Gems, Jewelry, art work, its value is its value. While you can argue that some of those gain value when created it starts from some value and improves somewhat. If it was made by crafting that means 1/3rd is raw material and the rest is skill improvement.
But a 25k diamond is 25k in materials. It *is* the same as gold. Don't let people make real world arguments, this is a game and we're talking about magic. Leave the real world and science out of this.
while magic is great it's not science.
Formal logic and such doesn't necessarily work on magic. It's a complicated business. That's why there's spell research.
Otherwise summon up some earth elementals to russle up some xorns to so they can tell you where their chache of diamonds is...
Otherwise it's hard work and science, geology, some digging or big presses and some physics and chemistry (even WORSE!).
turning gold into onyx, then onyx into diamonds is cute and makes no sense what-so-ever from a science viewpoint. While it may meet the requirements of Polymorph any Object, for all that spell effort it might be a 10GP to 250 GP gem of clear silica...
Advice adressing game balance:
from a game balance perspective it would be easier to turn 20000GP of platinum into 20000GP value gem. The trick is making money at it.
From a game balance perspective a spell should generate half of the NPC casting cost for that spell in GP value.
You can also use crafting rules setting the generic craft DC to the spell DC or an applicable craft/profession/perform skill that the caster has and kinda set the time to a week's worth of work or caster level in days. Fabricate, Minor Creation, Major Creation can give you guidance. I'll also mention a Lyre of Building, which is an old school item that replicates common construction work.
Again, when things get creative and you or players want to do something not in RAW but seems plausible, use Spell Research. It's a catch all for magical stuff where you don't say "No" right away and some discovery has to happen, which costs time and money. It also solves the metagaming issue of players knowing modern technology but their PC's don't. Let me refer to the (horrible) RAW Technologist feat requirement.
The wish spell has a cost of 25k GP because its not a spell any player should be casting often. You shouldn't allow any trick to work if it cheats this limit.
By the time you're flinging wish spells, finding a means of exchanging 25,000 gp for a 25,000 gp diamond ought to be child's play.