Recently a friend asked me questions about this subject. I do not claim to be a specialist. But I tried to be clear with him.
And here is more or less, what I told him concerning this subject, that seems at first glance very "odd" and fantastic. I made, already, an article about this subject here on my blog.
What is technically speaking an Homunculus ? It is a living form, made Alchemically, and able to live (more or less) by itself for a moment. In order to live, or bring Life, a form must be structured in order for its mercury and sulphur to sustain all parts of its body. Such form is submitted to cycle, and to a realm of existence, also to the laws of signatures.
For example, in his Munsus subterraneus (1665) Kircher, indicates that he made re-birth a flower from his ashes. Exactly like Paracelsus do with trees in one of his book. These are a kind of Homunculi.
But, to make appear from ashes a flower, an animal etc, in a mercury (like the "Universum"), is not at all the same thing, this is just an image in 3 D. Alchemy is a science in "3D" while a good Theurgist/Magus can also animate a picture easily (with the help of High Spagyrics), but it will stay flat, and not have the same impact at all. Of course, a theurgist can generate an entity, like I said in my previous article, but not really on the same level of existence, nor using the same laws.
This is a Palingenesis, a new Genesis from a pre-existent matter, this means that all kingdoms can have its own Homunculus. And of course, as the laws of Life are the same in the little world of Alchemy than in the Macrocosm, we have exactly the same kind of living entities... dendrites, crystals, plants, algaes, and animals, humans (maybe, for the last two, because it is very complicated I think, it is like solving the problem of the egg or the hen - which on came first ?).
I think that if someone try to create or generate, such a living entity, one should begin at first by the "lower realms", in order to understand fully the Laws and methods, the "how to", & "why".
I created, without intention such living entities in Alchemical process. A regeneration of a matter can do such things. I made several time such entities in the mineral realm, witnessing the birth of new crystals from an Alchemically prepared matter. Everything in total perfection. Nature is a living mechanism.
Another thing is to use very good materials, otherwise, you will not create a level of purity able to bear a higher level of Life.
Of course, the creation of an Homunculus is legendary, a little man or women, or even a couple in a flask is a kind of dream... but well, if I generated a kind of alchemical crystals in an alchemical world, in a flask, I could also generate a higher level of Life ... we are Homunculi in a big flask, called the "universe". It is not legendary, it is actually the world in which we live in !! Creating an Homunculus, whatever the realm can have a deep spiritual impact on you. Simply because you play the laws of Nature, as a Creator.
What you see *in* the flask, you see it *out* of the flask... it's an opening, a kind of enlightenment. But, you can only understand what you see with the eyes of an Hermetist. There is a life principle. "What is above, is like what is below". But one must be careful, and be psychologically prepared. Imagine you generate a monster in a flask ? What if it is like Frankenstein !? It can make you profoundly mad. Do not dabble.
The Philosopher Stone is said to have such power, to make flourish and born animals and plants from a totally virgin earth. But one can create such thing without the Stone.
I will not say it is easy, it is not, not at all. One must understand the Laws of Nature perfectly (sorry for repetitions but, it is really important), otherwise, one can go nowhere, and do nothing good.
What could I say more ... the production of the Homunculus is very close to the production of the Philosopher Stone. Creating an Homunculus can help for the Stone, and the Stone can help to create an Homunculus.
We are entering here in one of the domain of the Alchemical culture that is very little known, like a backstage, but you know, when we see wonders in Alchemy, "mind blowing stuff", sometime our limits are broken, and the impossible things can be a possibility for the initiated one.