An improvement is a crafted part you fit to one weapon: a sharpened edge, a new bowstring, a heavier head, or a coating on the blade. It adds to that weapon's bonuses for a number of hits or shots, then wears away. Most improvements are made from things you find early, so they are worth fitting from your first dungeon onwards.
Check what your weapon can take
Each weapon has one or more slots, and each slot holds one improvement at a time.
Edge and Coating: swords, knives, axes, spears, halberds, scythes, and pitchforks. A blade can be sharpened and coated at the same time. String: every bow and crossbow. Head: clubs, flails, morning stars, war hammers, staves, and canes.
Tools such as pickaxes, shovels, and saws take nothing, and neither do slings, thrown weapons, wands, or firearms. To see a weapon's slots, open its Info screen and look for the Improvements tab.
Make your first improvement
Improvements are crafted from the recipe list. Three need no tools at all and are the easiest place to start:
A Whetstone from two Stones and a Flint Stone sharpens a blade. A Hemp Bowstring from Rope and Plant fibre gives a bow or crossbow +4 ranged for 20 shots. A Sinew Bowstring from two Leather strips gives +1 strength for 15 shots instead.
Whetstones and Hemp Bowstrings also turn up in the dungeon. The Silk Bowstring needs a Needle, and the iron head fittings, Iron Spikes and the Weighted Head, need Iron Ingots, a Forge, and a hammer.
Fit it
Carry both the weapon and the improvement. A weapon lying on the floor must be picked up first, but an equipped weapon does not need to be taken off.
Open the weapon's Info screen and choose the Improvements tab. Each slot shows what is fitted and lists the items you carry that fit it. Choose Apply. Fitting costs 1 action point, so the tab is disabled when you have none left.
You can also start from the improvement: click it in your pack and choose Apply to followed by the weapon's name. Only weapons that can take it are listed.
The improvement now belongs to that weapon. It stays on it when you drop, store, sell, or trade the weapon, and a fitted string or head adds its weight and value to the weapon.
Know how much it gives
A Whetstone's bonus depends on your Craftsmanship: +1 strength at 0 to 2, +2 at 3 to 5, and +3 at 6 or more. It lasts 6 damaging hits.
Strings and head fittings keep the quality they were crafted with. A well-made one gives a larger bonus and lasts longer, and a poor one gives less.
An improvement's bonus counts as part of the weapon. A weapon in your off hand, or one you have not practised enough with, passes on only part of it, exactly as it does its own stats.
Watch it wear
The Improvements tab shows how many uses each improvement has left. Sharpening, head fittings, and coatings lose 1 use on each hit that deals damage. Misses and blows that deal nothing cost nothing.
A bowstring loses 1 use on every shot, hit or miss. No shot is fired without ammunition, so an empty quiver does not wear the string.
When an improvement runs out it is gone, and the hit or shot that used it up still gets its bonus. The weapon keeps working and wears its own durability as usual.
Coat your blade
A coating adds 1 point of elemental damage to each hit and leaves something in the wound. Burning Oil sets the target burning, Blade Venom poisons it, and Frost Oil slows it. Applying a bottled coating gives the Empty Bottle back.
Blade Venom is made from an Empty Bottle, a Venom Sac, and Animal fat. Frost Oil swaps the Venom Sac for a Frost Herb. A bottled brew that poisons can be spread on a blade too.
Burning and poison hurt an enemy at the start of each of its turns. If one kills it, the kill is yours, even if you have left the room. Coatings do nothing to NPCs and are not used up by hitting one, and against another player they cannot take them below 1 Health.
Swap or take it off
Applying a new improvement to a filled slot replaces the old one. The game warns you first, and tells you whether the old one comes back.
Strings and head fittings are hardware. Replace one or take it off with Remove on the Improvements tab, for 1 action point, and it returns to your pack with the uses it had left. Discarding the weapon returns them too.
Sharpening and coatings cannot be taken off. They are lost when replaced and lost with the weapon.
Armour takes improvements too
Armour and shields have their own slots, fitted the same way from the Improvements tab. Iron Studs and Reinforcing Plates add defence to leather, cloth, wood, and bone pieces, linings add warmth and never wear out, proofing adds resistance to ice, fire, or acid, and an Iron Rim strengthens a wooden or bone shield.
Your first improvement, step by step
Pick up a Light Crossbow or any bow, and a Rope and Plant fibre on the way. Craft a Hemp Bowstring. Open the crossbow's Info screen, choose Improvements, and apply the string for 1 action point. Load Wooden bolts and you have +4 ranged for your next 20 shots. When the tab shows the string running low, make another, and keep a spare in your pack.