You don't need oil, expensive products from other countries, specific paint brands, or any of the other misleading information out there. All you really need for cells is consistency.
To begin, choose several colors from the same high-quality artist brand, ensuring they have the same basic base and additives. Mix each color to the same thickness/consistency by using the same pouring medium—whether store-bought or homemade. Make them consistent by thinning the thicker ones to match your thinnest color. (It's much easier to thin paint than to have to thicken it later.) Start with a 1:1 ratio of paint color to pouring medium for each color, meaning use the same amount of pouring medium as paint. If, after combining, they all flow off the mixing stick at the same rate, you're ready to paint. If they are too thick, thin each with water or more pouring medium until they all flow evenly off the stick. This allows gravity to pull the heavier pigment particles down while the lighter ones rise to the top, creating cells.
The color in which you want to have cells should be applied over the other colors and should be slightly thinner than the rest. The reason is that pigments are the colored particles in paint that give it its hue. Different pigments have varying densities, meaning some pigments are heavier than others. The amount of pigment used in a particular color can affect its weight. White is very heavy, and that's why it sinks through the other colors so easily. Opacity of colors will also come into play, as transparent colors will show the other colors through themselves, but we'll get to that later in the blog. Remember, these are supposed to be fluid, so thin accordingly. The thinner your paints, the more they blend into each other, but if mixed too thin with water, it will break down the binder holding the color particles together, making the paint appear fuzzy or broken when it dries. It also won't adhere to the canvas very well, so thin slowly. You don't have to do it in drips; add a splash or two, and it'll be fine. If it seems like the color is too light in your cup, add more paint color and re-thin to match the other colors.
I'm not telling you not to try cell oils because I feel like you have to try everything to find out what works best for you. Still, I am here to tell you there are alternative methods that work better for much nicer cells, with less money and effort. I'll be putting together a list of the best alternatives for cells to try, so check back soon.