For many years my husband was a house painter. One of the toughest part of the job was painting kitchens because of the grease spots. Today we have a product that can be used to wash the walls and ceilings but in the 1800's this product didn't exist.
Here's a tip from Houghtaling's Handbook
Wash over smoky or greasy parts with salpetre, or very thin lime white-wash. If soap-suds are used, they must be washed off thoroughly, as they prevent the paint from drying hard.