http://swiftcraftymonkey.blogspot.com/2009/07/d-limonene-awesome-cleansing-power.html
Always combine equal amounts of d-Limonene and polysorbate 20. It's an oil based product, so the polysorbate 20 acts as your emulsifier to include it in surfactant mixes. Assume when I write "Use 5% d-Limonene" I'm also writing "with an equal amount of polysorbate 20" when it's a water based mixture.