Researching Existing Spells (CWH)

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In addition to researching new spells, a wizard can research existing spells (those listed in the Player's Handbook and—if the DM allows them—the new spells from Chapter 8 of this book). Since it makes sense that information about existing spells is easier to find than information about spells that do not yet exist, it is easier for a wizard to research them.
To account for this difference, make the following adjustments in the above procedures when a wizard is researching an existing spell:
# The Operational Cost is reduced to 100-600 (1d6 x 100) gp per week.
# The base chance of success is increased from 10 percent to 30 percent.
The lab costs, library costs, preparation time, and minimum number of weeks for researching existing spells are the same as research of new spells. The cost of increasing the base chance is also the same (2,000 gp per 10 percent increase), as is the total amount that can be spent (8,000 gp). Notice, however, that spending the 8,000 gp maximum increases the base chance to 70 percent (20 points higher than the 50 percent limit when researching new spells.)
==Limiting the Success Chance==
Notice that a wizard's chance of successfully researching a spell could exceed 100 percent, particularly when a high-level wizard is researching an existing low-level spell. Although automatic success is certainly in the spirit of the game (according to Table 4 of the Player's Handbook, all wizards of 19th level and above have a 100 percent chance of learning new spells), some DMs might prefer to eliminate any chance of automatic success. If so, we suggest requiring that all wizards must roll for success, even if their calculated chance exceeds 100 percent; a roll of 95 or higher is treated as failure.
==More About Magical Item Research==
Magical item research is discussed in detail on pages 84–88 of the Dungeon Master's Guide and needs little elaboration here. However, a few points are worth mentioning:
Laboratories: The laboratory requirements for researching magical items are different than those for researching spells. Spell research requires shelving, easels, writing tools, files, and similar supplies, while item research requires test tubes, beakers, burners, chemicals, and other equipment.           
Consequently, a wizard who invested in a spell research laboratory will still need to buy equipment to research an item. For example, assume that a wizard just spent 5,000 gp on a laboratory for spell research, and now wants to research a new potion. The basic cost for an alchemical laboratory is 2,000 gp (see page 87 of the DMG). Since the 5,000 gp laboratory is useless for potion research, the wizard must spend 2,000 gp for alchemical equipment.
Libraries: Just as a wizard's spell research lab is relatively useless for item research, so is his spell research library. However, a sizeable library of magical tomes probably contains short-cuts, hints, and formulas that will help the wizard in his item research. At the DM's discretion, access to a sizeable library (say, with a value of at least 74,000 gp) can increase a wizard's chance of success by as much as 10 percent. Access to a library doesn't change the amount of time it takes to research and create an item, nor does it change the amount of money that must be spent.
Specialist Bonus: If a specialist is researching an item that duplicates an effect of a spell from his school, his chance of success can be increased by as much as 10 percent. If the DM uses this rule, he should also deny a specialist the chance to research an item that duplicates a spell effect from any of the specialist's oppositional schools. The researcher's school has no effect on the amount of research time required, nor does it affect the amount of money that must be spent.