From Salem Wiki
"The Clay Trough can be used to make clay from dug out soil and Milk of Lime. Fill the trough with Milk of Lime, and right-click on it while carrying dug-out soil to make clay."
How to Make Clay
- Fill a bucket of water
- Add a Lime to the water to make Milk of Lime(you need solution with concentration 0,2% 2 pieces of Lime per bucket of water is enough).
- Pour Milk of Lime into the trough.
- Start digging any soil (need to have shovel equipped) until you get at least one clump of dirt (your character will be Shown carrying it above his head).
- Walk back to the trough and right click on it to start making clay from the dirt you are carrying, one piece at a time. Each clump of dirt dug up has a 100% to turn into clay as long as the tub has liquid in it, at which point you cannot continue and need to dump the remaining dirt.
- You may pour more than one bucket of Milk of Lime into the trough, and in fact this is highly advisable.
The Clay Trough holds a maximum of 10 buckets of Milk of Lime.
- One buckets of Milk of Lime can make 20 clay.
- Your character can carry up to 15 clumps of dirt if you keep digging to max capacity.
- A kiln makes a great storage container for extra clay, even if you don't intend to fire it up into bricks.
- Carrying a bucket of Milk of Lime will help avoid the situation of having your clay trough empty when making clay yet still carrying extra dirt.
- Clay Purity = Milk of Lime purity.