Edit: New information has been posted, check July 2014
The way this glitch works is by using up the very last material in your inventory, which by a glitch will leave you on an empty slot. From there you can mutate the empty slot into any grade 4 material ninty-nine times. (automatically makes it G4, the most expensive grade) Why I say 99x is thats the limit number you can have in one slot of the same type and grade. I'll explain by lettering the materials at first then give an example.
In the material bag, go to you last slotted item, this will be Material A.
No how much you have of A, make it into a multiple of 5 by selling or deleting.
(if you De/compress, you may add another slot which will ruin your attempt.)
Mutate A into a material YOU ALREADY HAVE, so there is no new material after A.
When you run out of A you should wind up on an empty slot B.
You will then mutate B, it will bring up Pack*7 Adventurer: 5 pieces
Do not hit "X" or Cancel, click continue, you will then be in the mutate menu in G4.
Mutate to the material you desire(If it's for Lars, go for Strong Cuirass/second row down, second last row right. It's 840ea.x99=83,160L)
Now that you have Material B, you can't mutate anymore because you only have one of this material.
Now go to another material ( C ) and mutate five Material A.
Mutate material A again to any random material YOU ALREADY HAVE.
You will be back on the empty slot, and mutate Pack*7 Adventurer: 5 pieces into Material B as much as you want!
Hope this helps, if some may need visual/picture reference. I can't uploading through my iPhone, so picture will have to wait.
Tags; Wild, Frontier, App, Wild Frontier, Wild Frontier App, Guide, Glitch, Unlimited, Unlimited Glitch, Grade 4