Purity affects only a few items in the game right now: Food items, Butcher's Knives, and Sabres. It has no effect on Inspirationals
Purity can add up to 10% to the damage done by a Sabre so that a 100% Purity Sabre does 110% as much damage as a 0% Purity Sabre.
Purity can add up to 100% to the value of a food, meaning that a 100% Pure piece of food gives 2x what its 0% version gives.
Purity is a measure of an item's AEther value. An item can have various amounts of AEther, Mercury, Sulphur and Lead, but Mercury, Sulphur, and Lead are considered Impurities and may have a use at some future date. For now, only AEther is useful. AEther is always 0 and Purity is therefore always 0% for items found in the wild.
Right now, there are several ways to increase Purity of the various industries in Salem so as to get better food and weapon purity.
Iron Purity has a direct effect on Sabre Purity and on Meat Purity through the Butcher's Knife and Hunter's Knife.
Iron Purity is increased by digging further from the ladder in a mine and by increasing the Mining artifice of your character's outfit. Boulders dug from the area near the ladder will tend to be low purity, though there is a RNG involved so that you can get lucky. Boulders dug further and further from the ladder will tend to be higher and higher purity with a chance of 100% at a distance of a couple hundred squares. Having a higher Mining artifice value in your clothing will give a bonus to the RNG so that purity tends to be higher.
Those who don't want to bother trying for high purity Iron can buy Bars, Sabres, and Knife Blades from other players and still get the benefits.
Sabres and Halberds can get their purity raised with Whetstone, Purity of the whetstone is then transfered to the weapon.
The purity of the Game Meat Food Group: Rabbit, Timber Rattler, Beaver, Deer, and Bear, is based directly off the Knife Blade used to make the Butchers's Knife, which must be held in the hand when butchering meat. The Argopelter Purity of the Poultry Food Group is also based of the Knife Blade. The Hunter's Knife, which can be bought from the store, can be have it's blade replaced with a Purity blade when the original wears off. Both a Butcher's Knife and a Hunter's Knife will wear with each butchering until the blade breaks and disappears. At that time, the hilt disappears, and the blade can be replaced.
If you don't want to bother raising your Iron purity, the Knife Blade is an item that can be bought from other players though it must eventually be replaced.
Much of the rest of food purity is based on Farm Purity. The Food Groups Bread, Maize, Pumpkins and Gourds, Vegetables and Greens, and Slugs Bugs and Kritters are all Farm Purity, as is Cotton Purity.
Farm Purity is based upon the Purity of the Field, the Purity of the Seeds, and a RNG which can increase or decrease the harvest by a few percent from what the average of Field and Seed purity should have made it. The lower purity seeds are very likely to increase when planted, while higher purity are more likely to decrease. Field purity, once it goes up, cannot decrease, so it is theoretically possible to raise it all the way to 100% and sometimes get 100% pure harvests.
This Purity grind does not benefit much from outside help. A field is limited to no more than a 1% jump in purity each planting, and even with high purity seeds, the resulting harvest will be very near to the purity of the field. The main way to raise purity of farmed fields is to simply keep harvesting and replanting on a regular basis and to mainly plant the better seeds that are harvested.
Those players who want the benefit of higher purity farmed foods can, of course, buy the ingredients from farmers who have good fields already.
Slugs Bugs and Kritters, which includes Slugs, Beetles, Caterpillars, Virginia Snail, and Turtles, can all be increased simply by picking up the creature and right clicking it on a pure piece of Cabbage Leaf or other Vegetable, but Cabbage Leaves are generally going to be the easiest to use. The creature will instantly gain the purity of whatever food it has been feed, whether that means an increase or a decrease, so be careful.
Farm Purity leads directly into Fish Trap Purity and Potted Plant Purity.
Fish Trap Purity
Fish Trap Purity directly transfers to the purity of the Fish and Shellfish caught in it.
Fish Trap Purity is based directly off the Fibre Netting used to make the Fish Trap. Fibre Netting can be made from any Fibre, but the only Purity Fibers available are Cotton and Milkweed Jute. The Purity of the Cotton Swabs or the Milkweed Jute will therefore determine the purity of the Trap when making a pure Fish Trap.
This is the only purity grind that can be basically skipped. The player can buy high purity Fibre Netting from anyone and so long as the Fish Traps are kept repaired, they will forever produce Fish and Shellfish of whatever purity their netting was made from.
The Gardening Purity grind includes Berries, Mushrooms, Nuts, and Vegetables and Greens (This group is based off Cabbage where the variable ingredients are concerned, but some other plants also count towards the Purity of the recipes. See Here for more details. General Tree Purity is also affected by Gardening Purity. The purity will be tranferred to the Nuts and Seeds and the Unscathed Woods found in a Coal Clamp and used to improve the damages made by the Blazing Braziers.
Unlike the other purity grinds, Potted Plants do not have a RNG, but are based entirely off an average of the Pottable, the Pot and the Humus.
The Pot's purity is like that of a Field, it will only increase and its ability to increase is limited to 2% per harvest, so buying and planting high purity pottables or using high purity humus will have a limited effect. However, once the pot's purity increases, it will never decrease.
The pot is an object which can be picked up, carried, and loaded into a canoe or sled, so it is possible for a player to buy or steal a pot from a player's base, and transport it across the map to another base. Of course, the risks involved are pretty steep.
The Humus purity is based on the Worms that make the Humus. Common Earthworm will increase Humus production efficiency by 6% and Earthworm Python will increase efficiency by 15%. At 100% Efficiency, the Humus will be equal to the average of all the Purities of the worms in the Humus Bin. So, with 100% Efficiency worth of 10% Purity worms, the humus produced will be 10% pure, if the Efficiency is 50%, the humus will be 5% pure. Worms will spawn in the Humus bins and affect the purity of the humus even if the Efficiency was already at 100%, so it is a good idea to check bins used for Gardening often.
Worms of both kinds always spawn at 0% purity and so they must be increased. Putting a worm in a box with food next to it will cause the worm to eat that food after a few hours and change its purity to be closer to the purity of that food. Foods that worms can eat include Any Plant, but the only plant they can eat which isn't a Pottable is Cabbage. In this way, Farm Purity directly affects Gardening Purity. Each time a worm eats a plant, it's purity moves 1/10 of the way towards that purity. So, if you feed a 0% worm with 10% Cabbage, it will receive a 1% jump the first time, a .9% jump the second time, a .81% jump the third time, and so on.
Because of the fact that worms will always lag slightly behind the Farm's purity, pottables will lag slightly behind worm purity, and pots will lag slightly behind the pottables, Potted Plant Purity will be able to approach 100% but never reach it. However, since the produce is always steady and won't RNG downward like the harvest from a Farm can, Gardening is more reliable in its purity.
Purity worms can be bought from other players and thus this purity grind does not have to be based on the player's Farm purity. However, those worms can't be fed better food unless it is bought from a player with higher purity fields.
Aside from Iron and Farm purity, Turkey Purity is the only other basic purity grind. The only other purity grind that does not depend on another industry's purity. Turkey Purity affects the Poultry Food Group, but only the Turkeys, not the Argopelters.
Wild Turkeys cannot have purity, but are designed so that newbies can use them for the Poultry Food Group until they are able to raise Domestic Turkeys, which have all the same bonuses and effects, only better.
Turkey Purity is based on the purity of the Coop, the Gobbler, the Hen, and a RNG. Like farms and pots, the Turkey Coop can only go up in Purity. It can raise by only .10% purity per egg laid, but a full coop of Hens can lay several eggs in a day.
Purity of the coop increases each time an Egg of higher purity than the coop is is laid. Subsequent hatching and growing up of the poult has no effect so it is okay to remove egg or poult from the coop to use in a recipe.
Purity of the Egg is significantly weighted towards the purity of the coop, so players wishing to skip this grind can only have partial success from buying pure Hens and Gobblers. The resulting eggs and hence the turkeys will be low purity until the coop has time to raise to match. However, they will still be higher purity than they would have otherwise been, and the coop will go up with each egg until coop purity matches Turkey purity so some benefit can be derived from buying turkeys.
How Food Purity Works
Each food belongs to a specific Food Group. When cooking that good, the purity is taken only from ingredients that belong to that Food Group. For example, Papricharred Charcuterie is a Slugs Bugs and Kritters recipe that requires a Raw Venison Steak, a Game Meat. I doesn't matter if the Venison Steak is 0% purity or 100% purity, the purity of the resulting food will be taken entirely from the Any Bugs portion of the recipe. However, that same Venison Steak's purity will matter in a Simple Sunday Steak, which is a Game Meat recipe.
When calculating Purity of a food, each individual ingredient is averaged first, then all the ingredient types that have an effect on the result are averaged. For example, a Berry Salad requires 2 Cranberry, 2 Blackberries, and 1 Huckleberries. If one Cranberry is 50% purity and one is 30% purity, the resulting Cranberry purity for that recipe will be 40%. If the Blackberries then average out to 50% and the Huckleberries are 60%, the three Types will be averaged together: (40+50+60)/3=50% total Purity. For Pemmican, the ingredients are 4 of Any Berries, 1 Raw Rabbit Cut, and 1 Gelatinous Lard. The purity of the 4 Berries is averaged together and that is the purity of the resulting Pemmican, no matter what purity the other two ingredients are.
The Berries Food Group receives purity from Cranberry, Huckleberries, Blackberries, and Crowberry Stalk. If the Dehydrated Berry, Pectin, Fruit Jelly, or Berry Jam is used, the recipe takes its purity from that as well.
The Bread Food Group receives purity from Flour, from Loaf of Ryebread in the cases where that is used as an ingredient, and from Sourdough Starters. In a way, the Starter is a mini Purity grind as it must be bought at 0% and when the resulting purity dough is 'Split', the starters retain the dough's purity.
The Corn Food Group receives purity from Corn, Cornmeal, and Corn Oil used in recipes.
The Fish Food Group receives purity from Fish and from Fish Filets.
The Mushroom Food Group receives its purity from whatever Mushrooms are used in them, very simple.
The Game Meat Food Group gets its purity from Steaks, Cuts, Meat Shreds, and Brains used in recipes. It is unknown whether Bones count as there aren't any Game recipes with them as an ingredient.
Nuts and Seeds receives its purity from whatever nuts are in the recipe: Walnut, Hickory Nut, Myrtle Oak Acorn, Stray Chestnut, Pine Nuts, and any Roasted Nut.
Poultry receives its Purity from the Turkey or Argopelter used in the recipe or from the parts obtained when cutting up a Stuffed Bird. Argopelter or Turkey Eggs also contribute their purity to these recipes.
Pumpkins purity is based on the purity of the Pumpkin or Pumpkin Flesh used in the recipe.
Shellfish purity is based on the Shellfish used in the recipe, whether it is whole, has had it's meat removed, or it has already been cooked.
The Slugs Bugs and Kritters Food Group receives its purity from the Caterpillar, Grub, Beetle, and Virginia Snail, and also from Wartbite Cricket and Frog both in their cooked, uncooked, and dissected states.
The Vegetables and Greens Food Group is a bit odd. It gets its purity not just from Cabbage Leaves, but also from other plants that are considered Vegetables. The complete list is unknown yet, but seems to include Carrot, Cooked Carrot, Oakworth, Grass, Ostrich Fiddlehead, Radish, Lilypad Bulb, and Milkweed Roots. All of these plants can be potted to raise their purity.