What does adding dish soap to acrylic paint do?

Adding dish soap to acrylic paint does several things, mostly as a flow aid and surfactant, but it can also affect durability if too much is used. A tiny drop of dish soap reduces surface tension of acrylic paint, making it flow more smoothly, improving leveling, reducing brush marks, and helping paint glide on surfaces, similar to commercial flow mediums. It can help paint adhere slightly better to slick surfaces like glass or plastic by acting as wetting agent, and can help prevent beading. In acrylic pouring and fluid art, dish soap is sometimes added to create cells and interesting patterns because soap breaks surface tension. However, adding dish soap weakens paint film, reduces adhesion, can cause foaming and bubbles, and makes paint less washable and less durable, as soap is not meant to be in paint film. Too much soap can cause paint to remain tacky, crack, or peel. So a very small amount, like one drop per cup of paint, can improve flow, but more than that harms durability. For best results, use proper acrylic flow medium or wetting agent instead of dish soap, as those are formulated to not weaken paint.