I've been meaning to add to this post for some time, but I have just not had the time until now. Already you have several excellent replies from people more qualified than me on many fronts. What I can add is my own experience on making absolutes (actually I only went as far as a concrete, but essentially the same except for the last step) at home using hexane. The short answer is it is both expensive and dangerous to do this, but it is possible. I did it because I was in a place (Burma) where I did not have easy access to absolutes by conventional means and there were some flowers in my garden where absolutes simply did not exist. Also after having tried many other methods such as tincturing and becoming frustrated by the fact water builds up in alcohol when folding tinctures of flowers are made. And hexane was easy to buy. With varying success, I made a concrete of 4 different things: 1) Gardenia, 2) a small indolic flower I don't know the English name of 3) Oakmoss, 4) Frangipani
In all but the case of the Frangipani I used small amounts of hexane (1 liter). For Frangipani I used 5 liters of hexane (and 5 times more flowers). On advice from this forum I proceeded by picking fresh flowers every day putting them in the hexane overnight, draining/filtering the the next day and putting in new flowers in order to saturate the hexane as much as possible. (you need two containers, in order to pour from one to the other and back. I would clean the alternate container completely after each day). This was the main process. I did this without any scientific way of telling them the Hexane was fully saturated. In the case of Gardenia I ran out of flowers as the season was shorter than my patience. The other limiting factor of this method is hexane loss, as some clings to the flowers each time they are discarded. This is unfortunate as you are losing both nice saturated hexane you have worked to hard to get and also the hexane itself, at $10/ Liter was being lost). A solution to this would be squeezing them out, but I wanted as little contact with the hexane as possible so I let the drip, sitting in a funnel, to get as much as possible, but far from ideal. I disposed of the toxic waste spent flowers by laying them out in the sun on the pavement to burn off as much hexane as possible before adding them to the gardener's "to burn" pile of organics. Also of note: some flowers (Gardenia and Frangipani) are quite "fat" and contain a lot of water, and small deposits of water developed in the bottom of the hexane containers. I used a pipette to remove this everyday once I realized it would contaminate the mix with potentially rancid water full of organics. Once complete I filtered the hexane solution through lab filter paper two or three times. The next step would be to run it through a rotary evaporator to both re-capture the hexane for later use and to separate out the concrete at a low boiling temperature. Unfortunately I did not have this. I consulted a friend who used to work in a traditional medicine extracting lab (hoping I could borrow a rotovap) and he said a group of Japanese technicians had the same problem, wanting to extract coffee flower concrete for their personal use. The low tech, and not ideal, solution offered to me was: Get a large beaker (the beaker spout is important as you will see in a moment), boil water far from your hexane and bring the pan to the beaker, now filled with your saturated hexane. Put the beaker in the pan of hot water (as in a double boiler). Put a plate or bowl over the beaker and fill this (plate or bowl) with cold water. Reheat the water as many times as necessary until all the hexane is out. The idea here I think is that the volatiles from the plants will stay mostly in the container and the hexane, being more volatile, will slowly bleed off into the atmosphere through the beaker spout. I did this outside as you can imagine due to the fact Hexane gassing off in the house is not a great idea on many fronts. This method has many drawbacks, from losing nice smelly volatiles, to the whole thing after weeks of work getting knocked over by the dog (or in the case of my garden in Burma, God knows what pythons, palm civets etc.) to the fact without a vacuum you will never really get all the hexane out and traces will remain. It also took an incredible amount of time this way. In the end, running out of patience, I got an extension cord and put the pan of water directly on an electric burner at low power (with the beaker in it still as in a double boiler of course). Nothing blew up (this is no guarantee it might not for you...). When handling Hexane I thought of it as gasoline in terms of danger and volatility. I also found the plate on top of the beaker to make the process take seemingly forever, and so I arrived at a compromise of doing it with the plate on for about 80% reduction, and the rest fully open, knowing I was losing precious smells, but really no choice unless I wanted it to take days. The results were really tiny amounts of some pretty nice stuff: from the 1 liter gardenia I got about 1 ml of nice goo, and from the 5 liters of frangipani about 10 mls of a very true to life (VERY sticky) concrete (which cost me $50 for the hexane alone, not to mention all the labor, equipment and electricity). Oakmoss was less of a success, I think I will go with a soxhlet extraction in ethanol directly next time (oh and the oakmoss was from my home in France, I brought it back to Burma to play with --in case anyone though I was saying there is oakmoss in Burma) The next step to make an absolute is to stir up the concrete in ethanol and then rotovap out the ethanol to get an absolute. This is (mostly) unnecessary for personal use (and I had no way of doing it anyway) and I just mixed the concrete in ethanol and filtered (many weeks later) and keep the ethanol concrete "tincture" for use directly as is. It was messy, time consuming, hard, dangerous and expensive, but I have moved from Burma now, and I treasure these concretes more than almost anything in my collection.
I am not recommending anyone replicate what I did, but hopefully me experience will help others.