While most spells and combat arts have grandmaster versions of them, only members can scribe them. If you go back to free-to-play again, you revert back to the highest level of the spell that you had scribed**. (**This may or may not have been changed to it reverting to master no matter what level it had been before. I've lost track of the changes since it was released.) If you then return to member status, the game remembers that you were GM'd in that spell, and you regain the use of it.
Example - Mum has a level 92 journeyman version of a spell. She happens on a lucky master find, and gets it turned into a grandmaster, then scribes the GM version of the spell. For one reason or another, her membership lapses, and she's back to using the journeyman version of the spell. When she re-subscribes, she can once again use the master.
Members can research masters to grandmasters in their knowledge book. It takes 40 days to research a level 95 spell from master to grandmaster. Yowie!
However ... crafters of all classes can obtain recipes to craft grandmaster spells. These can be obtained both by spell research and by drops. The recipes are broken down into four books per tier - fighers, mages, priests, and scouts. :D
Crafting grandmaster spells isn't cheap, though ...
First off, you're going to need the master scroll for the GM spell that you're making. Yep, you can see right away that there is NOT going to be a huge flood on the market of GM spells right away. ;D
Next, you'll need a spellshard or foundation. These are ultra-rare (rarer than normal rares) harvests from the appropriate tier zones. You cannot obtain these from your pack ponies, gathering goblins or guild harvesters, but only from manually harvesting. Spellshards are used for priest and mage GMs, foundations are used by fighters and scouts. Once the harvests are patched on Test/Beta, the following "should" be the breakdown:
n addition to the master and the spellshard or foundation, you'll also need 5 rares, 200 of a common resource, and 200 of the appropriate fuel.
The following are the recipe breakdowns, using the tier of resources appropriate to the level of the spell:
Want the ingredients spelled out a bit more clearly? Download the Grandmaster Recipe spreadsheet!