 Next, we're going to demonstrate a test for the presence of lipids. We're going to do this by adding two drops or two dropper fulls of water to one test tube, and then we're going to add a dropper full of water and a dropper full of vegetable oil to the other test tube. Next, we'll add Sudan four, which is the indicator for lipids. We'll put two drops into each test tube and we'll shake. Now, you can see that oil is indicated in this test tube because there's clearly a dark red layer, whereas in this test tube the Sudan is deposited uniformly. So Sudan has stained the lipid-based substance, the vegetable oil, a dark red.