I know you aren’t interested in products, but I took a slow and steady approach to letting my Dd use art supplies. At 2, to be independent and not make a mess, I had some colorwonder products and a water tablet...which is a board that you can color on with special pens that you just fill with water. She had unrestrained access to these at all times, no worry about mess. It wasn’t until 3-4 that I could give her other un-messy art supplies and not worry about some level of supervision.
In our house, when my Dd would get new art stuff, it would start in a cabinet that she had to ask to access and I’d supervise, then, if she could show she was careful with it I would let her use it without supervision, then if she was still careful, she’d get it moved to a cabinet that she could access on her own. Since she loves art, this was an ongoing process for us...crayons to markers to sharpies and fine line pens...color wonder to watercolor to tempera to acrylics...stickers to glue sticks to bottle glue...Glitter is not allowed in my house. Along the way she’d learn how to set up to use the medium, what she needed to clean and how, what could get stained, etc.
But, art was my dds favorite thing, so it was a daily activity and we always had some sort of art activity going, supervised or unsupervised.