Scrolls and Potions (DMG)

Just because a spellcaster knows a spell, he isn't automatically endowed with the knowledge to create a scroll or potion of similar function. The processes and formulae used in each are different.
A spell on a page in a wizard's spellbook is different from a spell contained on a scroll. The first requires memorization and may need components or gestures to activate. The latter needs only an utterance to be effective. A potion, ingested to be effective, is clearly a different form of the same thing.
Because of these differences, a wizard must learn more of his art before attempting to make scrolls and potions. He is assumed to have attained the appropriate degree of training by the time he reaches 9th level. Even then the knowledge of how to create such items does not just leap into his brain.
Rather, at ninth level he has the potential to create such items. He knows enough basics of the art and has learned where to look for the information he needs to make the attempt. The exact process for each spell is still a mystery to him.
==Scroll==
The first step in creating a spell scroll (not a protection scroll) is for the wizard or priest to know and be able to cast the appropriate spell—the desired spell must exist in his spell books. If he has never seen the desired spell or has failed to learn it, he certainly cannot create a scroll for that spell. When creating a protection scroll, the wizard is limited to those protective spells that fall within the purview of his art, for example, protection from elementals, magic, and petrification.
If a wizard knows the spell, he can begin fabrication. His first step is to assemble the appropriate materials: quill, ink, and paper. These materials can't be commonplace items lest they mar the final product or be consumed by the very magical energies the wizard seeks to enscribe.
The quill used for each spell must be fresh and unused. Lingering energies of the spell just transcribed cling to the quill. If the quill were used again, these energies would flow and intermingle with later attempts, causing them to fail.
Furthermore, the pen can't be just an ordinary goose quill. It must be from a strange and magical creature, perhaps one appropriate to the nature of the spell (the feather of a cockatrice for a flesh to stone, etc.). The task of gathering the right quill can be an adventure in itself. Quills hand-picked by the wizard himself increase the chance of success by 5%.
The paper or other material upon which the scroll is inscribed must also be of fine quality. Paper is best for this purpose, followed by parchment, and then papyrus. Each affects the chance of success as follows:
Paper 	+5%
Parchment	0%
Papyrus 	-5%
The ink is the final consideration. In this area, the DM has the greatest leeway to demand the most exotic ingredients and processes. The ingredients could be simple—the ink of a giant squid mixed with the venom of a wyvern's sting, or the musk of a giant skunk brewed with the blood of a gorgon. They could also be complex in meaning—the tears of a crocodile and a drop of water from the bottom of the deepest ocean, or a drop of mead from the cup of King Thyas blended with the lamentations of the women from the funeral of a great hero.
In general, the ink's ingredients should relate to the overall purpose of the scroll. As with the quill, the ink required for each spell should be different and even each inscription of the same spell requires the batch to be brewed anew.
After the character has gathered and brewed all the materials, he can begin the actual process of writing. Wizards must have their spell books at hand to guide their work, while priests and others must work on a specially prepared altar. The actual process of writing the scroll requires one full day for each level of the spell inscribed.
Protection scrolls require six days of work. During this time, the spellcaster must be undisturbed, breaking only for food and sleep (and then for a minimum of each). If the spellcaster halts before the transcription is completed, the entire effort fails and all work done to that point is for naught.
After the work is completed, the DM secretly checks for success. The base chance is 80%. This can be increased or decreased by the materials used. For every level of the spell, 1% is subtracted from the success chance, but every level of the spellcaster adds 1%. Thus, a 15th-level mage (+15) making a scroll of a 7th-level spell (-7), using papyrus (-5) and writing with a cockatrice quill plucked with his own hand (+5) would have an (80 + 15 - 7 - 5 + 5 =) 88% chance of success.
If the number rolled on percentile dice is equal to or less than the required number, the attempt succeeds. If the roll is higher, the attempt fails, though the player has no way of knowing this.
If the attempt fails, the scroll is cursed in some way. The DM secretly decides an appropriate effect based on the spell that was attempted. A failed attempt to create a fireball scroll may result in a cursed scroll that explodes in a fiery ball of flame upon reading. The player character cannot detect the cursed effect until it is too late.
Note: A remove curse spell will cause this faulty scroll to turn to dust.
A single scroll can contain 1 to 6 spells, the number determined randomly by the DM. The player can never be certain of the amount of space required even for the same spell on two different scrolls. A failed attempt to transcribe a scroll automatically fills the remainder of the page, although other spells successfully written before the failure remain. In this case, the cursed effect of the failed spell will not come into effect until that spell is read.
When using a scroll he himself has prepared, a wizard does not need to resort to a read magic spell to understand the writing.
==Potions==
Potions are primarily the province of wizards, although priests can prepare those potions relating to healing and cures. (Priests of other mythos may or may not be able to prepare such potions, depending on the spell spheres available to them.) Healing and curing potions are beyond the ken of wizards.
As with other magical items, the character must identify and gather the materials needed to brew a potion before he can begin work. The formula can be as straightforward or bizarre as the DM desires. It may require the blood of a rare creature, powdered gems, the sweat of a mare, or the breath of a dying hero.
In addition, a potion requires a number of mundane ingredients. The basic cost of these ingredients ranges from 200 to 1,000 gp. The DM should decide this based on how common the potion is, its power, and the nature of the ingredients he has specified. A potion of dragon control is a rare item of great power and so should cost the full 1,000 gp. A potion of healing is a fairly necessary item, something the DM may want to be readily available to the characters. Therefore, it should be cheap, costing no more than 200 gp.
Wizards must do more than acquire ingredients: They also need a complete alchemical laboratory. Potions are not something you can brew up over the kitchen stove! This laboratory must be furnished with furnaces, alembics, retorts, beakers, distilling coils, and smoldering braziers—in short, all the trappings of a mad scientist's laboratory (circa 1400 AD).
The basic cost for such a laboratory is at least 2,000 gp if all the skilled craftsmen are readily available to construct the equipment to the wizard's specifications. And this cost covers only the furnishings; the wizard must also have an appropriate place to put all these things and to conduct his work. Given the strange noises and foul smells that issue at all hours from such a laboratory, many a landlord may be less than willing to have his rooms used for such purposes.
Once the laboratory is established, the wizard must pay 10% of its value every month to maintain the equipment, replacing things broken in experiments and minor ingredients that lose potency with age.
Priests do not make use of a laboratory—such equipment smacks of impious and heretical learning. Instead, the priest places his faith in greater powers to perform the actual transformations needed to blend the potion. As such, he uses an altar specially consecrated to the purpose. When constructing such an altar, the character must be ready to make some sacrifice of worth, either a monetary sacrifice or, even more significantly, a special service to his deity. Thereafter, the priest need only respect the altar as would be normal for his faith.
Creating the Potion: With all this equipment assembled, the wizard or priest is ready to begin. The cost already determined, the time to brew, infuse, distill, decant, and extract the potion is measured in days equal to the cost divided by 100. During this time, the character must remain uninterrupted except for the normal needs of sleep and food. If the work is disturbed, the potion is hopelessly ruined as are all ingredients used in it.
After the work is done, the DM secretly rolls percentile dice to determine if the potion has taken. The base chance of success 70%. For every 100 gp worth of ingredients, 1% is subtracted. For every two levels of the spellcaster (or fraction thereof), 1% is added to the base.
If the percentile roll is equal to or less than the chance of success, the potion succeeds. If the potion fails, the spellcaster has unwittingly brewed either a deadly poison or a potion of delusion, at the DM's discretion. Of course, the player won't know whether a potion is good until it's too late. In any case, the wizard or priest is wise to label his creation, for there is no sure way to distinguish between different potions by sight alone.