Binding magic in the form of runes is no simple thing, and the creation of runic items is governed by certain unbreakable rules established by runesmiths long ago to avoid calamity. To represent this, all runic items in your army must abide by the following rules:
The Rule of Three: No single item can have more than three runes. No model can have more than three runes from each category.
The Rule of Form: No item can have a rune not intended for that item. For example, a hand weapon cannot have an Engineering rune.
The Rule of Pride: No two runic items in your army can be identical. This applies to items with only a single rune and to items with two or three runes.
The Rule of Jealousy: Each Master rune may only be chosen once per army. No item can have more than one Master rune.
The Rule of Duplication: Only runes marked with an asterisk (*) can be duplicated on the same item, combining together and increasing their effect.
It is also important to remember that a runic item is no different in principle to any other magic item, and that all of the usual rules for magic items apply to runic items as well.