Error in gnls(b0.5 ~ modelBlack0.5(v, w), start = list(v = 0.0075, w = 0.5)) :
approximate covariance matrix for parameter estimates not of full rank
There's a symmetry in the model, probably due to dilution bias.
I manually corrected symmetry in the data, but still see the same error.
Further scrutinizing led the discovery of a typo.
A typo in assignment that gave 'NA' bot b.05.max.