"Black as ink" is a common phrase used to describe something that is incredibly dark and opaque. However, there are several synonyms that can be used to give a similar effect in writing. One such synonym could be "pitch black," which refers to the darkness found in natural resin deposits. Another option could be "ebony" which is a darker wood material traditionally used for making expensive furniture. "Jet black" could also be a suitable alternative, which refers to the deep color of gemstones or coal. Lastly, "sooty" is another synonym to describe a darker shade which is often seen in charcoal or ash. By using these synonyms, writers can add more variety and depth to their language, making their writing more engaging and descriptive.