The surface of a worn die will sometimes become pitted, possibly as a result of decarburization of the die steel. These pits are expressed on the coin as low, flat elevations with relatively soft, irregular margins. Blebs are usually surrounded by obvious signs of die wear, such as radial flow lines or an orange peel texture. Blebs are usually found in the field.
https://www.coinworld.com/news/us-coins/unexpected-bumps-on-coins-surfaces-vary.html
As a die pounds away at thousands of planchets, the surface metal experiences microscopic plastic flow. Over time, the surface becomes rough. Radial flow lines, concentric flow lines, and an “orange peel” texture are names applied to various patterns of roughness.
https://www.error-ref.com/orange-peel-texture/
Die deterioration doubling (DDD)
DDD is the result of heavy die-use or improper heat treat (of the die) combined with die-use. Die-use eventually causes deterioration of the die steel and may manifest itself as doubling, thickening, twisting, “patches” and other deformities usually most pronounced on lettering or other designs closest to the rim but it may progress to more centralized areas in later stages. It is often found in combination with heavy die flow lines or irregular fields, (referred to “orange peel),”
https://conecaonline.org/glossary-of-error-variety-terms/