Your reflection reminded me of something C. S. Lewis once wrote, in defining Nature, which may be helpful here:
“I begin by considering the following sentences (1) Are those his natural teeth or a set? (2) The dog in his natural state is covered with fleas. (3) I love to get away from tilled lands and metalled roads and be alone with Nature. (4) Do be natural. Why are you so affected? (5) It may have been wrong to kiss her but it was very natural.
“A common thread of meaning in all these usages can easily be discovered. The natural teeth are those which grow in the mouth; we do not have to design them, make them, or fit them. The dog’s natural state is the one he will be in if no one takes soap and water and prevents it. The countryside where Nature reigns supreme is the one where soil, weather and vegetation produce their results unhelped and unimpeded by man. Natural behaviour is the behaviour which people would exhibit if they were not at pains to alter it. The natural kiss is the kiss which will be given if moral or prudential considerations do not intervene. In all the examples Nature means what happens ‘of itself’ or ‘of its own accord’: what you do not need to labour for; what you will get if you take no measures to stop it. The Greek word for Nature (Physis) is connected with the Greek verb for ‘to grow’; Latin Natura, with the verb ‘to be born’. The Natural is what springs up, or comes forth, or arrives, or goes on, of its own accord: the given, what is there already: the spontaneous, the unintended, the unsolicited.”
As for my two cents:
The ‘artificial’ is, I think, distinguished by the act-of-making — that is, by ‘factivity’. An igloo, say, would be just as artificial as a cabin built with hammer and nail. The hammer and nail are artificial: by your own assessment they are in fact ‘tools’. But hammer and nail are just as much made by human hands as an igloo is made by human hands. Indeed an igloo is itself a ‘tool’ after its own fashion; namely, a tool for shelter. In any case I submit that when the hands are employed in the act of making, say, an igloo, they are themselves being used qua ‘tools’.
Perhaps this is the real paradox? for at this point we might say human hands are ‘natural’ tools.