Creating your own gems is vital if you want to engineer a strong team. Unfortunately, gem crafting is probably the most complicated (and poorly-explained) aspect of Xenoblade Chronicles.
Above: Until you get a mobile furnace, Gem Man totally monopolizes gem crafting
The Gem Man’s Stall is located in the commercial district of Colony 9. Until you start reconstructing Colony 6 and obtain a mobile furnace, this is the only place where you can craft.
Gems are created from one or more of the following three things: crystals dropped by monsters, crystals harvested from ether deposits, or synthetic cylinders. All of these items have a rank between one and five, which correlates to the rank of gem they can be used to create. Once you reach a point in the game where you are finding the next rank of materials, feel free to sell off all materials of lower ranks; you’ll have little use for them.
Your goal is to combine up to eight materials at once. Once the percentage of one stat exceeds 100, you cannot add any more materials and must begin the crafting process (you can be clever and exceed 100 by a large amount, but we’ll get into the whys and hows of that later).
Above: When a man and a man love each other very very much, they get together and make lots of gems
The abilities of the characters you select will determine how the crafting process turns out; the affinity between them determines how many turns you’ll get. Which engineer you choose determines how frequently a certain flame will appear during the process. Which shooter you choose determines the bonus factor to be used during the process.
Each turn of the process involves either a strong, medium, or gentle flame. Strong flames greatly enhance a single attribute at random, medium flames moderately enhance all attributes, and gentle flames only increase the cylinder gauge.
At the end of the crafting process, any attribute value over 100 will automatically be converted to gem of the same rank as the materials used. Higher values lead to slightly stronger gems, though they cannot exceed the max strength of their rank. Easy enough.
Any attribute that does not reach 100% can be converted to a cylinder at the end of the crafting process - provided you filled the green cylinder gauge at least once. If you’re looking to create cylinders, use crystals that have multiple attributes, but don’t allow your desired attribute to exceed 100 during the crafting process, or they’ll automatically be converted to gems.
High-value cylinders are best used to push a value as far beyond 100% as possible in an effort to reach “heat” and “mega heat” states.
If you can push an attribute value to 200 during the crafting process, the number changes to the word “heat” and you’ll earn one gem one rank above the materials you used.
Although you can no longer see the attribute value after the heat state kicks in, it’s still there. If you can push it to 300 (very difficult), “mega heat” will be activated, and you’ll earn two gems, each one rank above the materials you used.
This is a random occurrence where you shoot several times during one turn. Unfortunately, it occurs very rarely, even with Shulk as the shooter.
Example 1: One gem and a cylinder
Let’s say we want to create one simple gem and one high-value cylinder for later use (such as in example 2). In this example, we’re shooting for an Ether Up gem and a Phys Def Down cylinder. We choose materials so that we have a high Phys Def Down value without going over 100 (remember, anything over 100 automatically becomes a gem).
For the crafting process, we choose Sharla and Riki. Since we don’t want to risk pushing Phys Def Down above 100, the fact that these two characters have low affinity and are only good at creating gentle flames works to our advantage: fewer turns means a lower probability of increasing the attribute values.
The result is no change whatsoever in the attribute values, giving us one standard Ether Up gem and a Phys Def Down cylinder with a value of 77. In advanced gem crafting, it is common to ‘sacrifice’ one value to make gem you don’t need in order to craft a cylinder of a specific value. In the above sample, we didn’t really care about the Ether Up gem or Chill Plus. Our goal was to create a high-value Phys Def down cylinder for later use, and that’s exactly what we did. It will come in handy when shooting for the “mega heat” state later.
Example 2: Mega Heat
This time, we want to keep things simple and achieve the best possible outcome of only one attribute: Ether Up. We’ve already carefully crafted three rank III cylinders for the process. To start, we choose two cylinders to get the percentage as close to 100 as we can without going over (96). This allows us to throw in a very strong cylinder at the end to push the value to 181 (remember, as soon as you exceed 100, you cannot add anything else). And since we are only dealing with one attribute, every strong and medium flame will work to enhance it.
Because we’re only concerned with enhancing this gem as much as possible, we choose Shulk, who has the highest chance at fever mode, as the shooter. For the engineer role, Reyn is best with a strong flame (which works to enhance one stat at a time, and we only have one) and also happens to have a very high affinity with Shulk, which means more crafting turns.
During the process, we get lots of what we want: strong flames. Throw in some very helpful party support (which is simply an affinity-based buff that happens at random) and fever mode, and we manage to reach a value of 300 (mega heat) and achieve two rank IV Ether Up gems. Note that even with our careful use of starting materials and the appropriate character roles, we reloaded our save four times before we got this very lucky result.