In reply to paul_the_northerner:
There is a lot of polish here on Portland limestone.
IMO, a lot of polish is caused by climbers (especially learner groups) walking about in their climbing shoes, collecting grit and sand on the bottom, then climbing, pivoting on their feet and polishing the rock. It is like having a pad of sandpaper on each foot.
We should be actively educating new (and existing) climbers to use a mat to change into their climbing shoes next to the rock and make sure the shoes are clean before they climb.
F1 drivers don't race with muddy tyres. Our expensive rock boots will stick much better if they're not covered in mud and grit.
The issue will only get worse as climbing becomes more popular. Once a hold is polished, it will take a looong time to weather back naturally.
Let's all start cleaning our shoes (where possible) before we climb