If it is not the case that the Teflon + glass pieces run gave a result between the other two, perhaps the next step would be to run the experiment again in the

If it is not the case that the Teflon + glass pieces run gave a result between the other two, perhaps the next step would be to run the experiment again in the glass vessels, but with pieces of Teflon in them. If Teflon is neutral, the results should match the glass-only run.