Encouraged by the who was phone water filtration thread, I figured I'd run a few ideas past you all. These aren't new things by most means, but perhaps by having the mechanics all together we might be able to hash out a workable system rather than proposing the same basic idea repeatedly. I'm not aware of any longstanding proposals with actual mechanics backing them.
The basic idea: structures which, with time and effort, refine large amounts of low q resources into small amounts of medium or high q resources. The "time and effort" part is important, to make sure it winds up being easier to trade with a village on a node than to do it yourself. Note that this wouldn't improve the node the raw inputs were taken from, but the materials themselves.
Global variables:
ref_n, the amount of refined product you get out per 10 units of input. Default 5.
q_mult, the basic quality multiplier. A q_mult of 2, for example, will be capable of eventually producing resources twice that of the softcap. Default 2.
Soil: Compost Bin
A 3x3 construction, mainly boards and blocks with maybe a little metal for hinges and such. Its behavior mimics the curding tub on a slower scale: you can dump fodder into it, as well as soil (which counts as ref_n fodder units). Over the course of an in-game week, it'll slowly spit out soil just as curding tubs do, at a rate of one soil per 10 fodder.
soil_q = (fodder_q + bin_q) * q_mult / (1+q_mult)
Water: Still
Stills have been proposed many times, so I'll just summarize: 3x3, built mainly from copper and branches. We should probably avoid requiring glass owing to the difficulty of acquiring good glass. You load it up with an input and fuel, which you need to maintain just like steel furnaces, and slowly (in-game week) it produces output, at a 1 in (10/ref_n) ratio. Output could be water and better water, or perhaps wine and aqua vitae, for purely medicinal purposes, you understand.
output_q = (input_q + (still_q + fuel_q)/2) * q_mult / (1+q_mult)
Clay: Sedimentation
IRL clay is processed, either by drying, grinding and sifting (aka herbalist table, quern, some constructed sieve), or more crudely, by sedimentation (a process which would be not unlike cheese-making). Since the former would be mostly easily-bottable stamina-limited grunt work, let me propose the latter.
The process: craft clay+1L water+jar = 1L clay extract. Put it somewhere, let it sit for an in-game week to sediment. Take it, pour into an empty jar to fill that with (ref_n/10)L clay extract of better quality. Degrade the remaining extract to match, or eliminate it altogether since it's nearly useless anyway. Eventually craft 1L extract with a linen cloth to receive 1 clay.
new_extract_q = (extract_q+water_q) * q_mult / (1+q_mult)
Clay_q = (extract+linen)/2
More scalable, but also more softcapped, and also requires good water. A fair trade, I think. If this isn't hard enough capping, maybe toss in a straining tub or some such step that would rationalize a block or board softcap as well.
Mathy example.
Say you can make a q30 bin, and you have q40 crops. If you make a bin and fill all 100 units with crops, in a week it'll make ten q46 soil. If you build and fill two bins instead, the 20 units of soil can fill a third (5 fodder each) for q50 soil in another week. Eventually you can get it up to nearly q60, which should be more than enough to grow better trees for new bins to increase the multiplier further.