I found a handy little Japanese webpage not too long ago in my internet wanderings that explained in detail how the day of the game week effects success rates on item synths. It was a bit hard to read though, so I translated it for my own use. Unfortunately, I can't find the web page again. However, I still have my translation I made, and I've decided to share it with you guys. I take NO credit for the following information, and give full credit to the Japanese web site I got it from. If I come across the site again, I'll gladly credit them here for their wonderful (and as far as I've been able to tell, 100% accurate) information.
The following is a chart illustrating the effect each day of week has with each type of crystal. The left column is the type of crystal you're using, while the top row is the day of week. The first set is your chance at a successful synth, the second set is your chance for getting a skill-up, the third set is the likelihood you'll manage to salvage your ingredients on a failed synth, and the last set is the chance of a HQ synth. Each "stat" is rated on a scale from one to four stars, one being the lowest chance or worst success rate for that category. Two stars is just an average chance of success. Three stars indicates a slight bonus to that category on that day, while four shows the best chance of success and a big bonus on that day of the week with that crystal.
Chance of successful synthesis:
| Fire | Earth | Water | Wind | Ice | Ltng. | Light | Dark | | Fire Crystal | **** | ** | * | ** | *** | ** | *** | * | | Earth Crystal | ** | **** | ** | * | ** | *** | *** | * | | Water Crystal | *** | ** | **** | ** | ** | * | *** | * | | Wind Crystal | ** | *** | ** | **** | * | ** | *** | * | | Ice Crystal | * | ** | ** | *** | **** | ** | *** | * | | Ltng. Crystal | ** | * | *** | ** | ** | **** | *** | * | | Light Crystal | ** | ** | ** | ** | ** | ** | **** | * | | Dark Crystal | ** | ** | ** | ** | ** | ** | *** | *** |
From that chart, we can see that the "safest" day to craft is on the same day as your crystal's element. The next safest days are either lightsday (always a good choice) or the day whose element your crystal is strong to. Darksday and the day your crystal is weak to are ALWAYS the worst days to craft, and all other days are neutral to your crystal. Light and dark crystals are an exception. Now let's look at your chances of skill-up.
Chance of skill increase:
| Fire | Earth | Water | Wind | Ice | Ltng. | Light | Dark | | Fire Crystal | *** | ** | *** | ** | *** | ** | *** | **** | | Earth Crystal | *** | *** | ** | *** | ** | *** | *** | *** | | Water Crystal | *** | *** | *** | ** | ** | *** | *** | *** | | Wind Crystal | ** | *** | *** | *** | *** | ** | *** | *** | | Ice Crystal | *** | ** | ** | **** | *** | ** | *** | *** | | Ltng. Crystal | ** | *** | *** | ** | *** | *** | *** | *** | | Light Crystal | ** | ** | ** | ** | ** | *** | **** | *** | | Dark Crystal | ** | ** | ** | ** | ** | ** | **** | **** |
Now this chart makes things interesting. All of the five "basic" elements have a very good chance of getting skill-ups on most days. The ones with four-star days have three "average chance" days, while the others only have two "average chance" days. I guess the four-stars are to make up for the extra average day. Anyway, light and dark break the rules as always. The really interesting thing is how everyone freaks out about darksday being so awesome for skillups, when for most crystals it's no better than most other days AND you run a significantly greater failure risk. This chart changed the way I look at darksday and now I avoid ever skilling on that day of the week. You don't really get any skill benefits with most crystals and you stand to lose so much in breaks and material loss. Speaking of material loss, let's look at that chart now.
Chance of saving materials on a failed synth:
| Fire | Earth | Water | Wind | Ice | Ltng. | Light | Dark | | Fire Crystal | ** | ** | * | ** | ** | ** | *** | * | | Earth Crystal | ** | ** | ** | * | ** | ** | *** | * | | Water Crystal | ** | ** | ** | ** | ** | * | *** | * | | Wind Crystal | ** | ** | ** | ** | * | ** | *** | * | | Ice Crystal | * | ** | ** | ** | ** | ** | *** | * | | Ltng. Crystal | ** | * | ** | ** | ** | ** | *** | * | | Light Crystal | ** | ** | ** | ** | ** | ** | *** | * | | Dark Crystal | ** | ** | ** | ** | ** | ** | * | * |
As you can see, lightsday is the only day that gives you any sort of bonus to material saves. Darksday is the worst day in the world for this one, and whatever day your crystal is weak to is just as bad. All other days are neutral to your crystal. So, we've established a theme that darksday is terrible for crafting thus far... Let's see if high-quality synths can redeem it.
Chance of HQ synthesis:
| Fire | Earth | Water | Wind | Ice | Ltng. | Light | Dark | | Fire Crystal | *** | ** | **** | ** | ** | ** | *** | **** | | Earth Crystal | **** | *** | ** | **** | ** | ** | *** | *** | | Water Crystal | ** | **** | *** | ** | ** | **** | *** | *** | | Wind Crystal | ** | ** | **** | *** | **** | ** | *** | *** | | Ice Crystal | **** | ** | ** | **** | *** | ** | *** | *** | | Ltng. Crystal | ** | **** | ** | ** | **** | *** | *** | *** | | Light Crystal | ** | ** | ** | ** | ** | **** | **** | **** | | Dark Crystal | ** | ** | ** | ** | ** | ** | **** | **** |
All crystals have two "best chance" days and two or three "good chance" days, except light and dark (which always seem to break the rules). And even here, darksday doesn't give any better chance of a HQ synth than lightsday most of the time. The day your crystal is weak to will always give you the best chance, as well as a second "freebie" best day. Your crystal's day gives you a good chance, along with lightsday and darksday. The day your crystal is strong to only gives you an average chance (with the sole exception of iceday). The only advantage darksday has over the others is it's a "best" day for three types of crystals instead of two.
So what does all this mean? Well, if you're looking for a successful synth, go with your crystal's day. You can also go with the day your crystal is strong to or lightsday, but avoid the day your crystal is weak to and avoid darksday.
If you want skillups... well, you're going to have a good chance of skillups more often than not, no matter what day you craft on. Days related to your crystal (whether it be your crystal's day of week, the day your crystal is strong to, or the day your crystal is weak to) will always give you a good chance, as will lightsday and darksday. Days unrelated to your crystal on the chart of elemental relationships are usually pretty neutral for skillups.
If you're worried about losing expensive materials and don't want to run the risk of blowing a lot of gil on a failed synth, your best bet is to craft on lightsday. Avoid darksday and the day your crystal is weak to like a plague if you stand a chance of losing a valuable ingredient in the synth.
If you want high-quality synths, either go with the day that your crystal is weak to, lightsday, darksday, or that random "freebie" day they give you.
Really, what it all boils down to is that lightsday is universally the best day for crafting since you'll always get some sort of bonus to any of the four "goals" you might be going for, and you won't ever take a penalty on lightsday (except under material loss with a dark crystal). Your crystal's day is another safe bet, since you'll get a bonus in three of the four categories. The day your crystal is strong to will give you a bonus in success and in skillups, and the day your crystal is weak to will give you a bonus in skillups and high-quality synths. Darksday is very bad for crafting because the bonuses it gives can be gotten from other days and without the same risk of failure/items loss.
So the next time your friends get all excited over darksday/new moon, you might point out to them that lightsday/new moon is much safer and just as good for most purposes, if not better.
I hope this chart has been of help to you guys, it took me about 100 years to get the formatting down and get everything colour-coded, which is why I've been putting off making this post. But I finally had some free time and decided to sit down and type all this out. I hope it's been of help to you, and good luck crafting (on lightsday ^_^)!
Edited, Apr 21st 2008 1:23am by Saboruto