Ink Stamping

This is on the base of a vase decorated and stickered by Salisbury

What colour is the stamp Heather?
Blue? Black? Purple?

I found a Salisbury type vase today with 18 stamped in purple on the base...
It looks like a Crown Lynn 18 ..... will put up a pic tomorrow.

Here are the photos...

Also to note....
I have found out that these are stamped using underglaze colours....
it looks like ink .... but underglaze would have to be fired when the piece was fired.

Sorry if I am dumb, but what does that mean?? Yes, that is the shape 18.

Stamps using underglaze colours/pigments/oxides are put on before the piece is fired.
This way the colour is fired into the clay and will never come off.

Though in saying that...... my stamp looks like purple ink ..... ?????
Ink would burn out if it was fired after being stamped.
What colour is the stamp on the 5 ??
Hard to tell from here maybe grey .....maybe black?

Blue I think.

I'm going to have to do a test with ink on something bisqued ....
see what happens.
Can you still buy ink I wonder?