Another D&RGW Water Tank Question

To All - My continuing search for information on the D&RGW water tanks has led to another set of questions. I hope someone can help.

It seems the most common finial that sat on top of the 50,000 gallon tanks was the ball. It sat atop an octagon shaped post, or pole, that ran down through the center of the tub.

Below the post, where it exits the roof is a "fixture" that undoubtably was put there to seal around the post and the roof. From the 1900 plans, this fixture measure 30" across at the outward (bottom) edge. It is installed on top of the roofing material, whether shingles or Elaterite, and completes the roof up the joint at the post.

This little "fixture" (if someone has a name that would be great) brings up some questions.

Some of the drawings also show that the fixture was octagon in shape. It this the case?

Was it made of wood (which it appears to be) or was was it made from metal flashing material?

If it was made from wood, was it painted or was it covered with flashing?

What color was the entire Finial painted?

As always, thanks for any data that anyone can provide.

Ken