If this happens, the item is left unenchanted, but the player is not charged any experience levels and can try enchanting it again. Very low modified enchantment levels can fall outside the ranges of all valid enchantments for certain items. All values obtained from 1.14.4 source code.

The maximum values can either be: the enchantment's minimum value plus a constant, the default minimum value of a generic enchantment plus a constant, or a constant level. The minimum values are all calculated using a linear function y = kx+m where y is the calculated minimum value, x is the current enchantment power level and k and m varies between different enchantments.

Note also that this is not just the base enchanting level provided by bookshelves you must also take into account the modification of levels that occur in step one. Or you can mine and gather the block itself such as diamond ore or coal ore (instead of getting diamond and coal drops). With this enchantment, you can gather items that are fragile and break such as glass or ice. These are not the levels you need to pay for an enchantment. The Silk Touch enchantment allows you to mine blocks themselves instead of getting the usual dropped items.

Minecraft how to get silk touch 1.14