On Fri, 3 May 2019 08:30:12 -0700 (PDT), wrote:

Looking round a house (with a kitchen refit done in 2013 and a boiler in 2010...) and came across some bare wire earths

https://flic.kr/p/2fGbsTq

What is the terminal block made of? Obviously before PVC. Was it
porcelain or that stuff with a rough feel that looked like a stone? It
doesn't look white enough to be porcelain.