[size=150](NOTE[/size]: This thread is a continuation of a previous tangent in a different thread. To read what preceded this, click here: Previous Off Topic Comments)
Alchemy is more, far more, than simple chemistry. With chemistry, any schlep can mix the right proportions and it all works out. With Alchemy, it requires training, an understanding of the Philosophiae behind the process, and at times an eye to the higher spheres to achieve the miracles of transformation.
If an alchemist does it, there is little practical difference. If you claim it's just "75 parts of saltpetre, 10 parts of sulphur, and 15 parts of charcoal of hazelwood, by weight", then you can also make a katana simply by folding metal 20 times, and an atomic bomb by gathering enough uranium together.
But it's just not that simple. Nor should it be.
There's a scene in the recent LotR movie, part 2 "The Two Towers", where Saruman is mixing a black crystaline powder that reacts strongly to open flame. But if you think that's "gunpowder", then why is he the only one who seems to be able to make it? Not just because it's "secret" - Orcs can work the process to make other orcs, and that's gotta be a secret too.
It's because it ain't that simple. If it was, it would be a very different world.
Interesting article on historical gunpowder etc.
anglosphere.com/weblog/archives/000123.html
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(After a bit of web research, to get facts straight and find some good references...)
The height of Alchemy was in the 16th century or so, and it was not until technology had to be accounted for that alchemy began to transform itself into what we, today, might recognize as chemistry. 13th century alchemy was purely based on an understanding of the higher spheres, spirits of the elements, the relationship of the 4 elements (and their inhabitants!) to the 4 humours, numerology, the outer spheres, and other important stuff that the uninitiated such as you or I just wouldn't understand, much less appreciate (or take seriously, ahem.) Doctrines such as the Emerald Table of Hermes, the idea of transmutation, and the Elixir of Life were studied and theorized upon, and experiments were based on those theories. Largely, alchemy was a philosophical pursuit, rather than a scientific one. Trial and errour played a tiny part, but after any failure the problem was viewed from a philosophical perspective, and once a "discovery" was made, it was not explained in terms of reactive materials, but again from a philosophical/mystical point of view, or to use the modern technical term, total BS.
Here's a good site that explains why Alchemy is related to Chemistry in much the same ways that, say, Fingerprinting is related to Phrenology, or modern Astronomy to Astrology - there is a cause and effect, but the later one did not evolve purely from the former, nor could ever be confused with them.
Alchemy is based in mysticism rather than what we, today, would consider "science". So, concepts like "The properties without reflect the spirits within" were more important than good lab technique or repeatable results. Since there are 7 planets, and 7 days of the week, there are 7 basic metals, and these are all related- thus, the good alchemist takes the astrological configuration into account, as well as his own moral and mental state.
Alchemy had no system, no unified theory, and no basis in "science". The "secrets" of alchemy were ritualized, and heaped with (to use the technical term) "mumbo jumbo" that only confused the issue, tho' remained critical from the philosophical perspective of the time. There was no widespread sharing of discoveries, or review of experiments that might disseminate even basic information.
From the above site, I got this list of things that we, today, associate with Chemistry, that Alchemy just doesn't take into consideration:12.1. Chemistry involves systematic identification and purification of substances
12.2. Chemistry seeks to understand the elemental makeup of substances[list] 12.2.1. qualitative analysis: which elements are present in a substance
12.2.2. quantitative analysis: numerical proportions of elements present in substances12.3. Chemistry involves the synthesis of natural and new substances
12.4. Chemistry seeks to understand the properties of substances and elements
12.5. Chemistry seeks to understand the nature of chemical reactions[/list:u]
The earliest known European recipes for gunpowder included many non-essential, non-reactive mystical ingredients, that were identical to those found in Asian recipes. The recipe was simply handed down, without question. No one tried any simpler recipe, because there was no "scientific approach" to suggest that such a difference would be possible.
An alchemist would be more concerned with how the planet mercury and the mercurial nature of some humans or animals would effect the material known as mercury, and pondering how astrology and, perhaps, discipline or training might change the way that a "mercurial" person could be changed with mercury - or something.
These diagrams should help clarify things:
THE SEPHIROTHIC TREE
Explanatory Figures
Helpful Tab III, outlining the Mysterium Magnum
Helpful Tab IV
The Key To Alchemy
Figure 6, a nice summation
Here's another site, where the above tables came from, with many historical examples of alchemical formulae and "secrets", including the Alchemists Prayer.
Here's an example of one formula written in the mid 1600's, when alchemy was beginning to look "more" like chemistry... 
[color=indigo]THE PROCESS--
[i]In the Name of God, take of the purest and cleanest salt, sea salt, so as it is made by the sun itself, such as is brought by shipping from Spain, (I used salt that came from St. Uber) let it be dried in a warm stove, grind it in a stone mortar, as fine as possible to a powder that it may be so much the easier dissolve and taken up by our Dew-water, which is thus to be had in the months of May or June: When the Moon is at the full, observe when the dew falls with an East or South East wind. Then you must have sticks about one and a half feet high above the ground when driven in the Earth. Upon two or three such sticks, lay some four square plates of glass, and as the dew falls it easily fastens on the glass like a vapour, then have glass Vessels in readiness, let the dew drain from the sides of the glasses into your vessels. Do this until you have enough. The full of the Moon is a good season, afterwards it will be hard."
The solar rays descending from the sun carry with them solar sulphur--the Divine Fire. These rays are crystallized by contact with the lunar rays. The solar rays are also met by the emanations pouring upward from the earth's surface and are thus still further crystallized into a partly tangible substance, which is soluble in pure water. This substance is the "Magical Mountain of the Moon" referred to in the R. C. letter. The crystallization of the solar and lunar rays in water (dew) produces the virgin earth--a pure, invisible substance, uncontaminated by material matter. When the virgin earth crystals are wet, they appear green; when dry, white...[/i]
(Von Welling makes a suggestion for the extraction of the solar life from stagnant water, but is reticent both as to naming the essence extracted and also as to the various processes through which it must pass to be refined and increased in power. His hint, however, is both valuable and unusual...)
"Take sweet clean water and seal it in a large bottle, leaving about one-fourth empty. Place the bottle in the sun for some weeks until it rots, showing a precipitation in the bottom. This precipitation, when properly manipulated by distillation, will produce a clear, fiery, burning oil, the constituents and use of which are only known to the wise." (???!!! 
)
The philosopher of Leyden continues: [i]"Now when you have enough of your dew close your glasses exactly, and keep it till you use it, that none of its spirits may evaporate, which may easily happen. Set it therefore in a cool place, that no warmth may come to it, or else the subtle spirit will rise and be gone; which will not so happen if after you have filled your glasses with Dew quite full, you close them very well with wax.
"Now in the Name of God, take of this Dew-water as much as thou wilt, put in a clean dissolving glass, then cast a little of your forementioned powdered salt into it to be dissolved, and continue to put it in till your Dew-water will dissolve no more or till the salt lies in it four days without being dissolved, then it has enough, and unto your Dew is given its proper powder. Of this compounded water, take as much as thou wilt, I took about a pound and a half, and put it into a round vial with a short neck, fill it with out water and lute it with a good lute, a cover and stopple that fits it well, that the subtle and living spirit of the dew may not fume away, for if they should the soul of the salt will never be stirred up, nor the work ever brought to a right end. Let the lute dry very well of itself, and set it in the furnace of B. M. to putrefy. Make a slow fire and let it digest for forty days or fifty, and that the fume of the water be continually round about it, and you will see your matter grow black, which is a token of its putrefaction.
"As soon as you have taken it out, have your dry furnace ready. Set your glass with the matter into an inner globe to coagulate, give it a slow degree of fire, continue it equally for twelve or fifteen days, and your matter will begin to coagulate and to fasten round about your glass like a gray salt, which as soon as you see and before it be two days, slacken the fire that it may cool leisurely. Then have in readiness your putrefying furnace as before. Set your glass therein and give the same degree of fire as before. Let it stand twelve days, and again you will see the matter resolve and open as before, and open itself, but you must every time see that the lute and your glass is not hurt. When you set your glass in the putrefying furnace, take care that the neck of your glass is covered with a wooden or glass stopper that fits it exactly, that the moisture of the water may not come at it.
"When you see it black set your glass as before to coagulate and when it begins to be of a grayish color and whitish, set it in a third time to putrefy, and coagulate to the fifth time, until you see that your water in its dissolution is clean, pellucid and clear, and that it appears in its Calcination of a fine white like Snow. Then it is prepared and becomes a Salt fixed which will melt on hot Silver plate like wax; but before you set this your Salt out, set it again [in] the furnace of putrefaction that it may dissolve of itself, then let it cool, open your Glass and you will find your Matter lessened a third part. But instead of your former Salt Water you will have a fine Sweet and very penetrating Water which the Philosophers have hid under very wonderful Names--It is the Mercury of all true Philosophers, the Water out of which comes Gold and Silver, for they say its Father is Gold and its Mother is Silver. Thus hast thou the strength of both these Luminaries conjoined in this Water, most true, in its right Pondus.
"Prescription. 5 Drops of this Water taken inwardly strengthens the understanding and memory, and opens to us most wonderful and sweet things, of which no man hath heard, and of which I dare not further write, because of the Oath I made God to the contrary. Time and the holy use of this blessed Water will teach us, as soon as you have taken it inwardly such influence will happen to thee as if the whole heavens and all the stars with their powers are working in thee. All Knowledge and secret Arts will be opened to thee as in a dream, but the most excellent of all is, you will perfectly learn rightly to know all creatures in their Nature, and by means thereof, the true understanding of God, the Creator of us, Heaven and Earth, like David and Moses and all the Saints of God, for the wisdom of our fountain of living Water will instruct thee as it did Solomon and the Brethren of our fraternity."[/i]
If any of this doesn't work, it's probably because you lost the "subtle spirit" (which may easily happen), or you misread the precise phase of the moon (and so it was hard) (whatever "it" is), or or you just didn't pray right, unbeliever. Sloppy alchemical technique, rookie mistakes, one and all. Try again, this time with feeling. (Or, for more secrets, send $5 to...) 
If you're still having trouble, I'll include one more diagram:
KEY TO THE GREAT PHILOSOPHICAL SECRET
aka the Figure conteyning all the secrets of the Treatise both great & small
No, no, don't thank me, my reward is the image of the look of comprehension on your faces.
So, V, in short, there were no "mundane" alchemists- it was all tied up with mysticism, spiritualism, higher philosophy and/or what otherwise might be called "magic", in that it ain't religion and you can't hit it with a hammer. There were craftsmen and trade workers, who made dyes or simple reagents or other compounds from traditional recipes, but the realm of mysterious research was truly esoteric and beyond anything "mundane".
And one very good reason why no one in Mythic Europe should invent gunpowder (or believe a recipe for it is legitimate) is that it doesn't follow any of the known principles- it just doesn't make sense to try.
[i](Tangent: I am confident in stating that there has never been a natural nuclear explosion, tho' evidence of natural nuclear reactions has been discovered. "Critical mass" causes reactions, "supercritical" causes explosions. Natural situations (usually the addition of water to a sub-critical configuration) would cause a reaction long before conditions an explosion could be reached, even if that were theoretically possible, which it isn't. An explosion would require a tight concentration of refined material, and natural material is, as a rule, not refined.
I was a licensed reactor operator in college for a while, and we talked about this very thing in the exhaustive NRC certification class. However, it's not inconceivable that something's changed since then - if anyone has a citation to the contrary, I'd love to see it- rather know I'm wrong than continue in ignorance.
V- see PM for more info.)[/i]