For those not familiar with NZR tarpaulins this photograph might help to show what Lawrence is trying to achieve. It looks like a 1930s view showing both traditional black dressed tarps (hot linseed oil and tar coated canvas) and 'modern' commercial canvas tarps. It also shows the grab handles well and truly covered by the tarps.
View attachment 266132
Tarps are very difficult to model convincingly so it will be good to see some convincing tarps on wagons.
The tarped wagon exercise has been slow as I waited hopefully for more information.
@Overseer 's exhumation of the Weston image led me to contact Culture Waitaki who came up with a scan at much better resolution for around a fiver (crop attached - Taylor’s Limeworks, c. 1930. Collection of Waitaki Museum & Archive, ID 6633P.
https://collection.culturewaitaki.org.nz/objects/106633/taylors-limeworks).

But to back up and review a bit: NZR sheets during the steam era were more or less variations on the black sheet of the second wagon, being treated with linseed oil/carbon black and stencilled in variations on that shown. At around my chosen period NZR were dabbling with other treatments and materials due to cost/convenience/supply matters.

I'm not especially interested in the subject as such, but to accurately portray tarps on the layout I needed some basis for their appearance at this time of flux.
The brand on the light tarp is 4/37, so the image is after that. The date of the correspondence is 1941 and the illustrated practice seems to be ongoing at that date, so I'm as happy as I'm likely to get that traditional black tarps are reasonable for 1940 stencilled as shown. The lighter tarps could also be represented, and now I know exactly what their appearance was.
No excuse not to move on, other than awaiting delivery of some decals for the stencilling. I can finish and paint the wagons though.