So, you want to make a potion or scared oil off the top of your head, do you? Potion making takes an understanding of what is in the ingredients and how they work together. Let's start with some basics.
Ingredients for potions and magickal oils come from flowers, trees, leaves, roots, berries or fungi. How they are collected can be important too: it can determine their power.
For instance, all the ingredients from trees have to be collected from deciduous trees in Autumn or Spring. For a tree, these times of year tell its that winter's coming and it's a good time to reproduce. A tree can be a very powerful ingredient for a spell, as it is the one that carries the energy from each season. So you want to have leaves or seeds from an oak tree in Autumn or Spring if you want some strong magic. That goes for any type of tree really, except evergreens.
Evergreens are very strong ingredients. The conifer family, pines, firs, junipers, cypresses and so on are nearly the strongest of all plants. Their power is in their resin, which can protect them from diseases or insect infestations. It also protects against evil energy. Resins and oils, such as frankincense or myrrh, work the same way. They can be very strong if your intentions are pure - so use with care!
Leaves are strong for primal energy, like if you want to make a gris-gris bag for protection or do a house blessing. They're also good in spells for purification, like white sage smudges. Before beginning your spell though, be sure that the leaves you collected are not poisonous or noxious.
With roots, consider that they have collected the energy of all the plants surrounding it over a long time. That makes roots very powerful - so use with care! As with trees, you can get magic from its leaves too! Roots are also good for primal spells, like grounding and protection. A root in your bath, for example, can purify you. A root is also good to use when building a house - place them under the foundation and it'll bring peace and increase fertility.
Fungi are very adaptable. All the ingredients from mushrooms have adaptogenic properties that help us adapt to negative energies or changes in our lives. They are also grounding.
Herbs are more complicated. Always look up their properties first. But bear in mind that some plants have similar properties or can be substituted for herbs of the same magics! For example, rosemary has many uses but is good with purification and protection. Chamomile works well as an alternative to rosemary, half of chamomile's properties are the same.
Getting the ingredients together is a good start. Make sure you know what they'll do and how to use them before you start putting them together to make a potion.
The next step in making potions is the oil. There are various ways to extract oils from plants - but there's one method that people use more often. You have to dry the flowers until they become crispy, then add them to olive oil in a closed container. Wait three days and strain out the petals before adding your herbs//leaves/tree bark. You can add them to the oil before the three days, but it won't have as much of a focus.
After that, you simply have to keep the jar in a cool dark place for a month and a half. Shake it daily. Then strain out your herbs and add any additional ingredients - things like rocks from a river bed or sand from the beach, moon water or blessed/purified water... The possibilities are endless!
Lastly is the base ingredient. This is often something clear - either alcohol, vinegar or water depending on what kind of potion you want to make. You can get really experimental with some potions though! For example, vodka has many properties similar to water but also some different ones too. It's good for energy making potions, while purified water is better for healing potions. A basic rule of thumb if you're playing it safe: oil potions go with alcohol and water potions go with purified or spring water.
Your herb/leaves/roots/mushrooms etc should be dried - no exceptions! And the oil you're using should be pure, not diluted.
Keep your potion in a cool place away from sunlight. A cupboard will do nicely, as long as it's dark and cool. And remember that sometimes you'll need to shake up your potion before use, depending on what ingredients were put together and for what purpose... But never make a potion without checking its properties first and thinking about how to use it! If you don't want to confess all of your secrets without knowing them yourself, make sure to ask someone who knows more than you about potions to keep you on the right track.