In mercerised fabrics, if patches are seen after dyeing, how can the root cause be identified-is it defective mercerisation or defective dyeing?

Generally, patches due to improper mercerising will be very distinct. They will invariably be darker than the rest showing very clear, sharp boundaries, unlike dyeing patches that would show a relatively diffused boundary. If patches are due to poor mercerisation, it would show up as a lighter shade and would distinctly appear 'un-mercerised' with dead cotton/nips showing up. Microscopic examination and Barium activity number will also help to confirm.