Johnson & Phillips Patent Liquid Insulator.
Johnson & Phillips patented their oil bath insulator in 1876 under no. 3534 and having 'Patent' impressed on it means this one must have been made on or after this date. I suspect its birth date is prior to 1900 as its made of stoneware not porcelain.
This example measures approximately 6in Diameter and 5.1/2in tall with a 2in hole underneath and originally cemented to a spindle
The base of the insulator curves up and under the bottom to form an internal groove. This groove was filled with oil to prevent small insects and spiders from making a cosy little home inside and as a consequence reducing its insulation properties.
The groove across the top is for wire retention, the wire itself passing over the top and usually another piece of finer wire was used to tie the main wire into situ.
The only markings found on this example is Johnson & Phillips Patent, impressed on its top front face
Bullers of Stock on Trent made a similar pattern for J&P in August 1882 and designated it No.41, catalogued as I 213 in 1882 and E.I 418 in 1885 . A similar shaped insulator was listed as being a Johnson & Phillips No.5, in a lecture given in 1878 to the Society of Telegraph Engineers by Mr John Gavey. However, I believe this was made by someone else, possibly J&P themselves.
Image courtesy of Mike Ashmore and the Beamish Museum