Soul urns are portable storage blocks, similar to shulker boxes. They have a lid which must be removed before accessing the contents. Right-clicking will remove the lid if it is closed. Right-click while sneaking to put the lid back on. Open soul urns will also act like a hopper, except they do not push items to other inventories.

Soul urns require a soul gem to craft. However, the type of soul gem has no effect on the urn.

Lidded vs Lidless

Soul urns normally have a lid which can be opened and closed. It is also possible to remove the lid completely. Placing a soul urn in a crafting grid by itself will allow you to change it into a "lidless" variety. Lidless urns are always considered open. Placing a lidless urn in a crafting grid again will restore the lid.

Colors

You can control both the color of the urn and its decorative gems. Soul urns will take the colors of the materials used to craft them at first, but this can be modified. Crafting with a gem will replace the gems. Crafting with dye will change the urn color. The mechanics are the same as leather armor, so you can combine multiple dyes to create any color you want.

Upgrades

Currently not implemented (at least in 1.13, I believe the 1.12.2 versions have capacity upgrades?) There will be an upgrade to increase capacity at the very least. Everything else is in the idea phase right now.

Some future upgrades may depend on whether the urn has a closed lid or not. For such cases, a lidless urn is considered "open", the same as an open lidded urn.