I'm not sure if this has been suggested before, and I don't quite know how to word a search for it, so if it's already been mentioned, I appologise, but anyway, here's the idea:
Certain reactions, and the creation of certain item types, could require a base level of general skill, in order to be available for use in your fortress.
This could perhaps be tracked by your fortress's "Guild Rating". The higher the guild rating for your fortress, in a given skill, the more options you'd have. This could also help introduce the idea of a "guildmaster".
Guild levels would be determined by *accumulated* experience, for all the dwarfs in your entire fortress. Living dwarfs would directly contribute their experience points towards the Guild's total.
Guilds might be formed when the total experience of all the dwarfs in your fortress, in a given skill, reached, say, 8100, since that's the experience required for 1 Professional in that skill. 12600 (Master) might raise it up to level 2, and 16100 (Grand Master) might raise it to 3, and so forth.
After 3, the accumulation of experience required to advance might become quite high, since we're talking about a pool of the entire fortress's accumulated knowledge of a given subject.
Higher levels might have a further requisite of atleast 1 Legendary dwarf in that skill, in order to advance to that level, with the assumption that part of the reason that dwarf is legendary in the first place, is that he/she invented complex process(s).
If a dwarf can read and write (another skill), they could continue to contribute their experience, even after they die, based on their level of reading/writing skill. To do this, you'd build a library, and each dwarf could then write a book about, say, cheesemaking, adding his/her cheesemaking wisdom to the accumulated Fortress lore. This would take time and resources, and books would only add experience based on whatever that dwarf knew when he/she wrote the book. New books could be written by the same dwarf, once they reached a new level of experience, but only the "best" book would count for that specific fortress.
The death of key dwarfs, or the destruction of your library, would subtract from your Guild Rating, and could be devastating to your fortress, atleast in the short term, encouraging the protection and care of all that powerful knowledge.
Other books could be written by your Guildmaster, on specific subjects, which would allow individual dwarfs to perform tasks that would be beyond their current Guild Level. So, you could have your Cheese Guildmaster describe how to make Munster (normally requiring Guild Level 2), and then you could sell it to another fortress. Or you could buy it from another fortress with a higher Guild Level. The book would then allow a dwarf *without* access to a level 2 Guild to make Munster cheese, but only that specific cheese, and only with the aid of the book, which would act as an extra tool required for the reaction (but which wouldn't be consumed).
The quality of these specific books might limit the quality of the goods produced-so if the Munster book is only Well Crafted, then other dwarfs reading the book wouldn't be able to make Exceptional Munster cheeses.
On the other hand, a dwarf who's only Proficient, but who can make Munster cheese, if that dwarf reads a Masterwork book on the subject, might get a bonus.
This would not only make books your fortress produced quite valuable, it would also encourage book trade, and would make books very distinctive from engravings.
To give an example of how Guild levels would/could work: creating raw iron from iron ore probably wouldn't require a whole lot of knowledge. You beat on a chunk of rich iron ore with a sledgehammer, and eventually it turns into workable iron. A little knowledge, a little skill with a hammer, and background information might be necessary to do it well, but you could probably learn it in a week, tops, even without a supervisor.
No guild rating required for this task, just 1 dwarf with "Dabbling" skill. It's something all dwarf parents probably teach dwarf children before they're even potty-trained, anyway...
Creating a specific type of mosaic patterned steel, on the other hand, is a complicated process that requires a lot of supervision, and a lot of experience. It's partly art, and partly science. The first time you try it, even if you're being helped by someone who knows what they're doing, there's a good chance that you're not going to end up with an ideal product.
So, while almost anyone with a good strong build can be taught to make plain, soft iron, efficiently and well, it takes a lot of experience and a greater level of knowledge to make the patterned steel.
So making fine mosaic steel might require a Guild rating of 5, for example.
The same goes for more complicated goods. Brewing beer is fairly straightforward, whereas brewing an Imperial stout is a lot more complex, requiring more skill, and an accumulation of knowledge. It doesn't matter whether it's an "average" imperial stout, or a "masterwork" imperial stout. Without *some* skill in brewing beer, you're going to screw it up.
Being able to dictate the level of skill required to "open" a specific reaction for use would not only be interesting, but it would be a great way to balance more advanced materials and products.
It would also be thematic, since more advanced fortresses should be able to produce more advanced goods, due to an accumulation of skill over time, rather than just lucking out in finding raw materials, and these advanced products would make trade more interesting between fortresses, and give you the option to specialize.
Getting back to cheese (what? I like cheese), you might, for instance, found a fortress that has poor mineral worth, but really good grazing pasture. So you could raise cows, sheep, goats, camels, whatever, and make cheese to trade with other civs. So you set out to make a nice farmer's cheese, and you trade your farmer's cheese for iron, lumber, whatever.
Farmer's cheese only requires a single dwarf with "dabbling" skill.
Since cheese is your main export, you assign more and more dwarfs to making it.
After a while, your cheesemakers have accumulated enough skill and confidence to make feta cheese, which is a little more valuable, and can be made from goat and sheep milk, only.
This requires a Guild level of 1, and is an event that marks the formation of the "guild entity" itself.
At this point, though, it's little more than an informal club. It's basically a shared hobby.
Your cheesemakers become more knowledgeable, and after a while, you move on to Blue cheese.
Guild level 2--At guild level 1, your "guild" is an informal affair, and members meet at the local pub. Other people call them "cheesegeeks", and nobody pays them too much attention, but every cheesemaker knows every other cheesemaker, atleast by reputation, and they share knowledge openly.
So you make that, and trade it for weapons and armour, and maybe some copper for jewellery. Eventually, your cheesemakers have the skills necessary to make roquefort cheese, which is similar, but even more valuable than blue, and can only be made from sheep's milk, so you can only make small quantities of it, but it's valuable enough to trade for gold and silver.
Guild level 3--At guild level 3, they're gaining some respect in the community, they have rules and regular meetings, and it's time to build a guildhall.
At this point, your Guildmaster would actually be elected.
Finally, your Master Cheesemakers, after years of experimentation, are able to make Gorgonzola, which requires an elaborate process to make, involving cow's milk and specialized cheese cultures, and it needs to be aged in a cave, but that you can trade for gems.
Guild 4--The guild is a minor, but significant part of the fortress, and is starting to develope real economic power. It's forming alliances, establishing trade with other fortresses, and consolidating it's power. The guildmaster is a well-known, and respected member of the community, and people buy most of their local goods, from that guild.
At level 5, The economic power of the guild is firmly established, and it's goods are a vital part of the fortress's economic strength. The guildmaster is becoming more and more of a political position, and is well-known, even among the aristocracy.
Level 6. Your guildmaster will either be granted a noble title, or purchase one, and will promptly become as annoying as any other noble, making demands not only for his/her office, but on behalf of the guild itself. Assassinating the guildmaster is an option, but it comes with repercussions--you'll lose not only the guildmaster's accumulated experience, but (temporarily) their ability to write book guides, and the guildmaster *will* be replaced, sooner or later, unlike many other types of nobles.
Level 6 and higher guilds not only represent the increasing sophistication of goods, but also how renowned your guild is, how famous and desireable it's goods are, how far away it trades, and eventually, it will even have the power to enforce laws and standards on it's trade partners.
In this way, a skill that may seem very ordinary, or even unnecessary, like cheesemaking, with very humble beginnings, could eventually have a significant role in the history of your entire world, and shape the very character of your entire fortress.
One thing your Guild could do would be to claim origin of a specific product. This could require that a dwarf in your fortress produce a Masterwork of that product, before anyone else does.
For instance, if your fortress "Mountainbreaks" was the first fortress to produce, say, a Masterwork Stilton, it might at Guild Level 9 claim a "protected designation of origin", meaning that, from that point on, all 'Mountainbreaks Stilton' would be considered the original, "real" Stilton, and would be more valuable than anyone else's stilton-maybe +1 base value for all "original" goods.
This could work by adding +6 to the Guild Level needed to make a specific good. Since Stilton might require 3 Guild Levels to make it, by Guild Level 9, if yours was the first fortress to produce Stilton, then your Guild would have the political power, and the public renown, to enforce the claim that your fortress is the origin of all Stilton.
Artifacts-in certain cases-might preempt all that, so that by making the very first Artifact Stilton in the world, even if your Guild Level was only 3, you'd automatically get "origin" status for Stilton.
Ofcourse, not every single artifact produced would convey origin status, but it might be one effect an artifact *might* have.
Now, mechanically, the fortress's "guild level" is just the requirement for making the basic items. Levels of quality for specific items would still be determined as they currently are.