The Seven Metals

Usually the great Work is divided in three stages according to the three principles colors: black for Nigredo, white for Albedo, and red for Rubedo. But there is another system that divides the Great Work alongside this threefold system, and that is the one of the seven metals or planets which must be interpreted according Greek mythology.
Nothing is so confusing as the seven metals in alchemy. In some manuscripts the name of metals is used alongside other symbols. Sometimes the metals are described a bit more in detail. often it is difficult to figure out if it is about laboratory work or purely symbolic.
In Dictionnaire mytho-hermétique Dom Pernety (an 18th century French writer, Benedictine, librarian, and founder of a secret society) defines the use of the seven metals in hermetic alchemy as follows: "When the Wise talk about metals, they do not understand these objects that are in use in everyday life; one must understand them in the sense of that they talk about the transmutation of imperfect metals in gold or silver. Their metals are only different states of their mercury in the operation of the work. These states are seven in number, like there are seven Planets and seven common metals; this is the reason why they give the system of their work to the seven Planets, which rule at every state, and every dominion manifest itself by a different color. The first state is that of mercury, which comes before the black color. The second is that of Saturn that lasts all through putrefaction until the matter start to become gray, that is when the Wise call their matter lead of the Philosophers. The third is that of Jupiter, son of Saturn, who was subject to his voracious father, who mutilated him in order to prevent the ability to procreate: his mutilates parts were thrown in the ocean and they gave birth to Venus, by which one understands that the black color does not appear anymore in the work. And because Jupiter was the father of the gods, with Junon, represented by the air enclosed in the vase, and the humidity which mixes itself with it.
"The entire dominion of Jupiter is used to wash the milk, what happens by the successive ascending and descending of mercury on the earth. That water represents the sea, Of which the flow and reflux is marked by these ascensions and continual descensions. But the Philosophers have another sea, that one will see explained in his item.
"The Poets gave to this milk the name of Latone, mother of the Moon and Sun; because the moon period is a continuation of the ablution of the milk, that by there becomes white, and of a whiteness bursting as the one of the Moon. Venus dominates next, and this is in the time that the matter takes a citrine color, that goes over to red, or of iron rust color, and thus comes the period of Mars, friend of Venus, that lasts until the color orange, represented by the dawn, before sun comes up. Phoebus, brother of Diane, appears at last under the crimson color. The Poets said that Diane his sister played the role of midwife to his mother Latone when she gave birth to the sun, because real gold, or real sun of the Philosophers, would never appear until the white color, or Diane, had not appeared beforehand. By all this one can easily see how many Mythological hermetici are mistaken in their arbitrary explanations of the Fables, as this is only a allegory applied to the Great Work".
This might be a bit difficult to read and understand if you are a novice to alchemy. After all, you are supposed to be knowledgeable about the different Greek mythological tales. The hermetici in past ages were familiar with Greek mythology because it was their prime source for understanding the human condition and their world view. They understood that the myths were symbolic and allegoric.
In a nutshell:
1. Mercury, planet Mercury: the substance, the Matter to be worked on. originally you have to find out what it is. For the Hermetic Alchemists it is of course you yourself, what includes your body, your mind (=emotions and thoughts) and your divine essence.
2. Lead, planet Saturn: the beginning of the state of Blackness. The Matter is putrefying and dissolving.
3. Tin, planet Jupiter: the color gray that appears at the end of the process of Blackness, when the Matter has been purified to almost a perfect white. Jupiter is the son of Saturn, therefore he is the next stage.
4. Copper, planet Venus: the citrine color. Venus is the next stage because she was born when the testicles of Jupiter, cut off by his father Saturn, fell into the sea.
5. Silver, the Moon: the white color, corresponding to the state of Whiteness or Albedo. The Matter has been completely purified. In Greek mythology the Moon is symbolized by the huntress goddess Diane. Diane is the daughter of Jupiter and Latone.
6. Iron, planet Mars: Mars is the friend and lover of Venus. Orange or rust-red color, like the light of dawn. It is the state during which the Matter starts to become red.
7. Gold, the Sun: this is the last state; the red color or Rubedo. Here the Matter is called Red Sulfur, among other terms. The sun god Apollo.
As the Hermetic Philosophers were well versed in ancient mythology and derived a lot of their symbolism from it, it might be interesting to note that the use of the seven planets as a progression in the Great Work has a stunning parallel in Gnostic teachings. The Gnostics explained that man here on Earth lives basically in a spiritual darkness. Through initiation he ascends through seven layers/worlds created by the Archonts to eventually arrive at the eight sphere where the initiate will shine in all its divine glory. The seven spheres were associated with the seven traditional planets, and they were each a hindrance to the progress of the spiritual person. It is remarkable that the alchemists also talked about passing through seven stages of the Great Work, each associated with one of the seven planets.
 

The seven metal/planets in images: