What happens to objects, changed while transmuted using Minor Alchemy, after they revert?

Question

If the form of an object is changed while it's transmuted into another substance with the Minor Alchemy wizard ability, do the changes last after the effect wears off and the object reverts to its original substance?

We recently dealt with a hole that was too small due to rocks blocking either side by using Minor Alchemy to change one of the rocks to wood, then burning the wood away. This widened the hole enough.

Should this have worked? Does a rock transmuted to wood count as wood for all intents and purposes, including being able to burn? When the Minor Alchemy wears off, what form would the "burned away" rock return to? Would the wood just not burn in the first place and eventually return to being a rock?

Other uses we came up with that gave us pause:

• Transmuting copper to rock, crushing the rock into gravel, then waiting until it reverts to copper to get shards of copper.
• Wood to copper, melt the copper, and cast it into the desired shape to get wood in odd shapes.

Answer 1

They remain as they physically are after reverting, as logic and rule interpretation dictate.

The feature's last sentence specifies that when it ends "the material reverts to its original substance", mentioning no physical deformation at all. Moreover, there is no mention of the temporarily changed material having any unusual properties (such as stone->wood being unable to burn).
Essentially the ability causes a chemical mutation, not a physical one, both when it is used and when it ends. What that means is that the material's form will not be affected, not by the feature's initialization/end at least.
In your particular first example it would be reasonable to describe the wood as burning properly and then the produced ashes turning into powdered stone, as if disintegrated perhaps. The smoke would become heavier and be similar to that grey fog that you see around mines, very thin particles of stones hovering in the air.
The DM would be free to dictate any specifics on such cases as no rule seems to cover them extensively (and it would probably be impossible to do so without lots of complex definitions and phrases not required in a game of fantasy and abstraction).

One could argue that a very popular similar effect, the Flesh to Stone spell, unlike the feature under discussion, does mention how the target retains any physical alterations caused to it while transmuted to stone. I strongly believe that the lack of such a passage from "Minor Alchemy" is not a hint for different behaviour. Rather, it would be more appropriate to assume that the passage specifically exists in Flesh to Stone because it targets creatures which would bring more discussion/confusion upon missing, in comparison to the Minor Alchemy case.

As a final note, I would consider such usages to be rather interesting and creative when it comes to overcoming challenges for the players and would seem rather fitting (theme-wise and as a power level) for the Transmuter subclass. I would advise DMs seeing such applications to not feel intimidated by them but rather welcome them in their story as appropriate.

Answer 2

So I think these things you have come up with are perfectly reasonable. In fact, it sounds like a great idea for an artisan character concept that makes impossible structures out of wood. Hey maybe that's how you make wooden fullplate for your druid.

The transmutation requires a lot of time (10 mins / cubic foot) & it only lasts for an hour. It doesn't make things permanently more valuable unless you are an artisan, so its greatest power may be destruction. Exactly as you did, to make an object easier to destroy.

I guess its other great use is ripping off merchants by converting all of your copper pieces into silver pieces, but that doesn't seem like a great long term plan.

At the end of the day, this is exactly what I like about role-playing, using magic and cunning in creative ways to solve problems.