It sounds like the pattern has the appearance you should be seeing after 6 cycles or so using this method.
It normally takes me at least 12 but usually around 15 cycles to get a nice deep color to the pattern.
It builds up slowly as you're loosing part of the built up color on the softer iron portion of the pattern each time you etch as well as completely removing it from the harder steel composition of the bbl material.
If you do choose to boil it now you will most likely instead of the faint brown/white contrast,,get a faint black/white contrast. Sort of like the first coating of rust blue.
Some bbls work up faster than others it depends on the iron and steel content, the rust soln you use, the rusting time, etch soln and time in the etch,,ect.
Most everything you do is a variable upon the completed look.
For that reason, when excellent results are obtained, the finisher tends to stick closely with that process. But there are many different ways to obtain the right look.
Ask 10 different people doing the work and get 10 differing ways of doing it.
Results are what matter.
