
Demon Stolas is described in the Goetia, in the Pseudomonarchia Daemonum, in The Discoverie of Witchcraft and in a few other old Occult books.
Below you will find useful information about Stolas and hopefully this information will help you to summon Stolas.
Demon Stolas: Goetia
Stolas is the 36th spirit and he is ranked as a Prince. He appears at first in the shape of a large raven, but he can take on human shape too.
Stolas teaches astronomy and helps you to discover the properties of herbs and gems. Stolas commands 26 legions of spirits.
Source: Goetia
Stolas: Pseudomonarchia Daemonum
Stolas is a prince and he shows up in the form of a raven. Later he takes on human shape. Stolas teaches astronomy and helps you to know the properties of herbs and gems.
This spirit rules 26 legions of lesser spirits.
Source: Johann Weyer, Pseudomonarchia Daemonum
Stolas: Daemonolatry Goetia
Summon Stolas if you want to learn Witchcraft or if you desire to learn science (biology, botany, geology, etc).
Source: Daemonolatry Goetia by S. Connolly
Similar demons
Sustugriel from Grimoirium Verum can teach you any magick if you are a beginner student. Sustugriel can teach you more advanced magick if you are an advanced practitioner. Sustugriel taught me how to summon the spirits of the Arbatel.
Astaroth taught me magick with the planetary talismans. These talismans are described in the Golden Dawn and also in the Three books of Occult philosophy.
Samigina taught me the magick of Kabbalah very fast: he taught me the Hebrew alphabet, rituals, the theory of White and Black Kabbalah, how to draw seals and how to summon both angels and demons. Samigina introduced me to a magickal order in Stockholm too.
Asmoday teaches technical stuff like code and software. Summon Asmoday together with Amaymon during one and the same ritual.
Stolas: when to summon him?

So, first, lets note that Stolas is a Prince. Take a look at the Princes and Prelates of the Goetia and you will discover Stolas among those spirits.
The Princes and Prelates of Goetia, including Stolas, are summoned during Thursdays, because the planet Jupiter rules Thursdays. Also, it would be great if you can summon Stolas during the astrological hour of Jupiter.
I use the correspondences of Chesed even for Gamchicoth:
Ruling planet: Jupiter
Day: Thursday
Astrological hour: Jupiter
Paper seal colour: blue
Metal: tin
Gems: sapphire & amethyst
Number: 4 (4 candles for example)
Plant: olive (use olive oil)
Scent: cedar (I use cinnamon)
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