First of all, crossing two breeds together doesn't mean the offspring are pure. They are neither Orpingtons nor Plymouth Rocks. They are mixed. So you can't call the Plymouth Barred Rocks either.
Second of all, Lavender is recessive (and dilutes black). None of the F1 offspring will be visually Lavender. In order to be Lavender, a bird must have two copies of the gene. Like their father. Since he is only able to give one copy Lavender) of the gene to his chicks and the mother only gives one copy (Black) of the gene to her chicks, the chicks will all appear Black with barring.
Barring is more complicated and hens only need one copy to be barred while males need two.
@The Moonshiner or
@Amer can explain that way better than I can. I don't fool with barred birds.