Old Jewels
In the continent of MU different jewels are used to upgrade the various items in-game. Some jewels are sold at NPCs, some are dropped from MOBs and some must be created.
Jewel of Bless
One of the most important jewels in the game. Used to upgrade items up to +6. No chance of fail. Can be stacked to piles of 10, 20 and 30 for easier trade and some chaos combinations. It is also used for making Potion of Bless.
Jewel of Soul
Another important jewel in the game. Upgrades items from 0 to 9 but has 50% chance to fail. On fail from 0 to 7 downgrades the item with 1. On fail from 8 to 9 downgrades the item to 0. It's also needed for upgrading items until +13. Items with "Luck" have 75% success chance instead of 50%. Can be stacked to piles of 10, 20 and 30 for easier trade and some chaos combinations. It is also used for making Potion of Soul.
Jewel of Chaos
This is the most sought after jewel in game. It is used in all item combinations except for putting pink options.
Jewel of Life
Upgrades the normal option of an item with 50% success rate. On fail reduces the option with 1 level.
Jewel of Creation
Used for creating fruits that increase stats and resurrecting pets. Also used for the socket system and nowadays, a very useful jewel for clearing PK status, registering for PVP Last Standing Event and registering for marriage.
Jewel of Guardian
Jewels of Guardian are used for upgrading Castle Defenses and creating Life Stones. Also used to add a "pink" option to special items.
Jewel of Harmony
Jewels of Harmony are used for adding a "yellow" additional option to your items. It is one of the ingredients of seed making too.
Lower and Higher Refining Stone
Used for increasing Harmony (also known as "yellow") Options.