1. The substrate, precisely
Not "plastic" but ABS, PP or PET; not "metal" but aluminium or stainless steel. Coating chemistry is matched to the exact surface, and the difference between PP and PC is the difference between a system that bonds and one that peels. A photo of the part helps more than a paragraph.
2. The finish you are imagining
Gloss or matte, opaque or transparent, soft touch, glitter, pearl, crackle, metallic. Reference photos work; a competitor product works even better. The closer the target is described, the fewer sampling rounds it takes to hit it.
3. Honest volumes
Monthly quantities decide everything downstream: batch sizes, price per litre, and whether a dedicated shade is practical. A supplier who knows you need two hundred litres a month will spec differently, and better, than one guessing at ten thousand.
4. Your line and cure conditions
Do you have an oven, a UV tunnel, or neither? What line speed? As we covered in 1K stoving versus 2K PU, the right chemistry is chosen by the line it must run on, not from a catalogue page.
5. Where the product will be sold
Export markets bring compliance requirements: REACH screening for the EU, TSCA for the USA, food-contact rules for anything that touches consumables. Saying "this ships to Europe" up front lets the supplier build compliance in from the first sample; Colortek's ISOTRAP and METACOAT carry SGS-verified references for exactly this reason.
Then let the lab do its work
With those five answers, a formulation can be matched, a sample produced on your own substrate, and a decision made on evidence. That is the whole process, and step one is one message.
A photo of the part helps more than a paragraph describing it.