Zinc Passivate, bad finish

Have just bought bright zinc passivating kit, we do lots of small parts but only 4/5 at a time, minimum order costs are prohibitive. Round steel disks 50mm in dia. have followed instructions to the letter, but finish is very poor compared to getting a shop to do it. not shiny at all. What is the best way to get the parts chemically clean, acid dip? But in what? How long should the parts be in the plating tank for? and how long should they be dipped in the passivating solution. Instructions say 3/4 hours in the plating tank and 10/15 seconds in the passivate.

I've been involved in zinc plating in the UK for over 30 years and have no idea what a 'zinc passivating kit'is. Where did you buy it? In the first instance I suggest you get back to the supplier. I'd be reluctant to offer any advice on the information you've provided.

The simplest answer and probably the cheapest is to have a 2 year supply done by a good shop. It is still probably a min lot order.