Tinting a spotcolor does what to Lab values?

Is there some way to precisely predict what a printed 50% tint of a spotcolor ink will look like, i.e. its Lab value?

The Lab value of 100% patch of that spotcolor ink is exactly known.

Is a 50% tint the average of the Lab 100% value and say (100 0 0)?

Perhaps it is the average of the 100% Lab and the Lab of white.

Is the relationship linear?
I would think it might be since Lab is linear preceptually, and dot percentage I think is also linear.

This doesn’t appear to be ANYWHERE!
Any help is appreciated.

Wow. Interesting question.
To be able to do this you would need spectral measurements, not Lab measurements. You would also have to know something about the opacity of the ink used, and also factor in the optical brighteners in the paper. Then, since dot gain would not be linear, you’d have to take into account that when you ask for 50%, you will actually be getting something else (say 60%).

So, no - we don’t know of a way to do this in a mathematical formula sort of way.