Almost all items, as well as many game-world objects, have a quality factor Q, which may range from 1 to ∞, with a standard default quality for most objects of 10 -- for example, all natural-growing trees are Q10. In general, higher Q items are simply better: high Q weapons do more damage, for example.
The in-game effects vary from item to item, with some items like buckets and linen clothing not having any effect at all. Where quality matters, it usually takes the form of the quality multiplier QM:
This multiplier is 1x for Q10, 2x for Q40, 3x for Q90, 4x for Q160, and so on. It is a nonlinear increase, which just means that it becomes harder and harder to get a good multiplier for higher and higher multipliers. Since Q10 has a QM of 1x, in many places on this wiki you will just see stats given for Q10 objects. You should assume this unless the wiki page you're reading says otherwise.
To make higher-Q objects, you should use higher-Q materials with higher-Q tools. Some materials, like in farming, have a natural quality "spread" of ± 6 points, which you can use to grow higher-Q foods. Others, like soil, fish, water, clay, and herbs, have a Q determined by a natural (but invisible) hot-spot on the map. In other words, you might find that one day you forage a Q31 Spindly Taproot. This means that this square has Q31 soil. If you dig around in a 5 square radius, you might be able to find higher and higher Q soil -- perhaps even Q40 at some square. You could then mark it off for later, as you can always come back to that hot-spot to collect high-Q herbs, soil, and earthworms. You might then use that soil to plant high-Q trees, which will help you make high-Q tools.
It is very common for crafting qualities to be softcapped by a crafting skill or a vital stat. For example, if you have a Q40 bone and a Q10 branch, you can in principle make a Q35 bone saw -- but if your survival skill is lower, perhaps at 15, you will only make a Q25 bone saw, because (35 + 15)/2 = 25.
It is also very common for fractional qualities to be rounded down to the nearest integer.
There is still much to be understood about the quality system. Use this section to discuss findings, theories, etc.
Quality of crafted goods can be dependent on any (including combinations) of the following: Quality of ingredients, crafter's skill level, and crafter's stats. Which of these three are used seems to vary from item type to item type.
Armor and Clothing
Backpacks and cosmetic clothing are unaffected by quality.
Armor gets increased HP and AC as its quality increases. The AC gets multiplied by QM, while the HP gets multiplied by Q/10.
- Leather Armor: 150 HP, AC 25/25 (2R)
- Bear Cape: 50 HP, AC 0/15(1L and 8L)
- Chainmail Shirt: 475 HP, AC 75/75 (2R)
- Bronze Plate: 500 HP, AC 100/100 (2R)
- Plate Armor: 500 HP, AC 150/75 (2R)
- Leather Boots: 100 HP, AC 0/20 (8R)
- Leather Pants: 150 HP, AC 25/25 (2R)
- Ranger's Boots: 150 HP, AC 15/15 (8R)
- Druid's Helm: 225 HP, AC 30/10 (1L)
- Hirdsman's Helmet: 200 HP, AC 45/20 (1L) Only usable by Hirdsmen within a village.
- Boar Tusk Helmet: 120 HP, AC 5/30 (1L)
- Soldier's Helmet: 425 HP, AC 50/25 (1L)
The FEPs given by a piece of food get multiplied by QM. So, for example, a Q10 beetroot gives 0.5 PER and 0.2 CHA, but a Q90 beetroot will give 1.5 PER and 0.6 CHA.
Quality does not affect the amount of hunger that the food restores -- just the amount that it buffs up your vital stats.
There is use for low quality foods, as they can be eaten for FEP Reduction as the FEPs given relative to higher quality foods can be negligible at higher levels.
The quality of structures is not affected by who builds them or what they are repaired with.
Seeds quality is affected by your farming skill and reduced by it if its lower then the crop's Q.
Water recovers more stamina per hunger as its quality increases. Details unknown.
> Q 10 water goes at a rate of 5% per 5% hunger
> Q 65 water goes at a rate of 15-16% per 5% hunger
The quality of crafted items is equal to the average quality of the ingredients rounded down. However, it is also capped by the appropriate skill level of the crafter. Different items have different weights in averaging the quality of a final product. For example, a Q50 bone combined with a Q10 branch would make a Q20 arrow, because a bone weighs 2 and a branch weighs 6. (The formula would be (50*2 + 10*6) / 8) - These are not the true weight values of these items, these are example values. 
Cooking and Ceramics
Cooking and pottery are both very similar. When you bake, you produce a dough based on the average Q of your ingredients, softcapped by the square root of your Cooking*Perception. You then place this into an oven, which requires fuel. The quality afterwards is given by a weighted average:
Pottery uses the same formula as well: the only difference is that you craft a ceramic based on the average Q of your clays used, softcapped by dexterity. Then the ceramic is the "dough", the kiln is the "oven", and the fuel is still the fuel.
- Quality for all accessories except monocles and spectacles is equal to the quality of the Goldbeater's Skin, softcapped by .
- Monocle and glass quality is the average of the materials, softcapped by smithing
- Bear Tooth Talisman quality = tooth quality, softcapped by psyche
- Bone saw quality = (5*qBone + qBranch)/6, softcapped by survival
- Traveller's Sack quality = qHardened Leather, softcapped by sewing.
- Board quality = sqrt(qLog * qTool), softcapped by carpentry
- Woodblock quality is simply log quality. Your Carpentry and stone axe don't matter.
- Leather quality = (3*qHide + qBark + qWater + qTub)/6.
- Quality for all full metal products are calculated with the formula: quality = (qMetal*4 + qAnvil*1.5 +qHammer*1.5)/7
- Smithy's Hammer quality = (qMetalQ*3 + qAnvil)/4
- Cheese quality will be equal to that of curd quality, softcapped by cheese tray quality
- Butter quality = (4*qMilk + qChurn)/5, softcapped by cooking
- Butter-steamed Cavebulbs are affected by butter, water and cavebulb quality (not by fuel though)
- Beer quality = (qWort + qBarrel )/2
- Fish quality = Fishing spot quality, softcapped by (qPole*qLine*qHook*qLureOrBait)^(1/4)
- Grape juice quality = (3*qGrape + qWinepress)/4, only last pressed grape matters
- Wine quality = (qGrapejuice + qBarrel) / 2
- Vinegar quality = (qWine + qBarrel) / 2
Sewing limits: quality affected by dexterity
- quality of leather items
- quality of cloth products
Smithing limits: quality affected by strength and sometimes psyche
- quality of metal working recipes (sqrt(STR*Smithing))
- quality of jewelry recipies (sqrt(PSY*Smithing))
- quality of crafted wooden items e.g. boards (blocks are only affected by tree quality), cheese trays, Primitive Dolls...
Cooking limits: quality affected by perception
- quality of cooking recipes
- quality of unbaked goods - If PER is lower than the average quality of the ingredients, quality = [PER+ 2*(ingredient 1) + ... + 2*(ingredient n)]/( 1+2*n), otherwise it's just said average.
- seeds when harvested (MaxQuality = farming +5)
- quality of flour ground at a quern
- quality of trees
- arrows, bone saw
- quality of foraged items
- skinning and butchering; quality = (Animal Quality + Tool Quality + 2*Survival)/4.
- bone quality only affected by survival.
The effect of survival is capped at 300.
- quality of bows
For buildable objects, the quality is almost always calculated as such:
- The qualities of items in the individual item types are averaged arithmetically.
- The resulting average qualities of the various types are also averaged arithmetically -- often with some weights on items that should be "obviously" more important (like the iron in iron plows) -- to create the quality of the built object.
For craftable items, most are calculated like this:
- As with buildable object, the qualities of the individual item types are averaged, and then weighted together based on importance.
- If one is using any tools, like a churn, anvil, or smithy's hammer, the qualities of those are averaged with the above resultant quality -- often with a weigth of 1/4 for the tool.
- If any character attributes are involved, those attributes themselves are averaged geometrically, and if the resultant "skill quality" is lower than the "input/tool quality", the resultant quality is the arithmetic average of the skill quality and the input/tool quality.
If you don't know what a geometric average is, it is the multiplication product of the individual values, raised to the power of the inverse of the number of values. In other words, averaging values geometrically means calculating .
As for ovens, kilns, smelter and finery forges, the quality of the resultant quality is the arithmetic average of the input item quality and the average of the oven quality and fuel quality, where the fuel quality is the arithmetic average of the fuel items put into the oven. In other words, if the item quality is , the oven's quality is and the fuel's quality is , the quality of the resulting item will be .
As for the skills involved in crafting, it should mostly be obvious, but there are, of course, a few things to clarify:
- Sewing related recipes (including leatherworking ones) use the Sewing and Dexterity values.
- Smithing related recipes often combine both Smithing and Strength.
Calculate items used:
If there's a tool involved:
If there are skill values through involved:
- Calculations will be made in order of top to down.