hoodoo charms and ritual materials--and grimoires (including the famous Pow Wows, or The Long Lost Friend) alongside cosmetic and medicinal items.
In the world of The City, catalogs like these are handy resources for material components and materia magica. Even in more traditional, pre-industrial fantasy campaigns these materials might be used to add some flavor to spellcasting. For campaigns that don't use material components, maybe these materials enhance the potency of spells?
Here's a selection of some of the materials offered in the catalogs with suggested D&D game effects. Example spells affected for each material are from the Open Game License System Reference Document version 3.5.
Devil's Shoe-String: Thin, flexible roots of a family of plants related to honeysuckle. These can be used as components in spells to "tie up" or "hobble" enemies (Entangle, Hold spells, Slow, Snare) and also be carried for luck in gambling.
Goofer Dust: Made from graveyard dirt, powdered, shed snake-skins, sulfur, and salt in the main, exact goofer dust formula's are trade secrets of the various manufacturers. Goofer dust is sprinkled where an enemy will walk, or perhaps placed inside his shoes, and leads a magical poisoning. [On a failed saving throw, the victim suffers a -2 to penalty to attack rolls, saves, and ability checks for a period of 1-10 days.]
Graveyard Dirt: Dirt acquired in a graveyard can be used as a material component for some spells which do harm to others (Bestow Curse, Cause Fear), but can also be used in spells of protection (Various Protection and Magic Circle spells). Whether graveyard dirt is gathered by the would-be caster or bought from a supplier, care should be taken that it has been "paid for"--usually by leaving an offering of a silver piece in the graveyard--to appease the spirits of the dead.
Lodestone: Pieces of naturally magnetic iron ore. Lodestone is a component used in spells of luck (Locate and Find spells), or attraction (Charm and Summon spells). Some hold that different color lodestones have greater potency when used for specific purposes.
Four Thieves Vinegar: An ancient, Old World formula, this is a mixture of herbs and vinegar, which can be ingested or applied topically to provide resistance to disease and magical protection. [Adds a +2 to saving throws against disease, and a +1 against spells for 2-12 days with each application.]
Van Van Oil: Made from herbal essential oils, it may be applied to the body or a surface as a component of spells of protection ([Alignment], Magic, Arrows, etc.). It can also be used to anoint magical items like amulets or rings to enhance them, or weaken cursed items. [Application of the oil adds one additional charge (1 time/item) to an item with limited charges, adds a bonus to the effect of any non-charged item for 1-10 hours, or removes the deleterious effect of a cursed item for 1-10 hours. These last two effects may be gained more than once per item, though never in a cumulative fashion. The oil has no effect on scrolls, potions, or magical weapons or armor.]
For information on real-world hoodoo and rootwork, and more examples of magical materials. check out Cat Yronwode's great website.
16 minutes ago