Before you lighten or bleach your client's hair, it is important that you explain the process and effects of doing so. Use this waiver (client consent) form for your clients!
Technical manual, technical document, whatever you may want to call it - here are links to the technical documents of big hair brands like L'Oreal Professionnel, Pravana, Goldwell, and many more!
Free for you to access and use, they are especially useful if you need to familiarize yourself with a colour line that you are new to.