Identification
ID in this catalogue WCO 1
Type Outflow water clock
Current Location Egyptian Museum, Cairo
Catalogue Numbers JE 37525
Provenance Burial cachette in the court of the seventh pylon at Karnak (Legrain (1906), 65)
Date Amenhotep III, 18th Dynasty, New Kingdom
Dimensions

External: height 34.5 cm; upper diameter 46 cm; lower diameter 26 cm

Internal: height 30.6 cm; upper diameter 44.4 cm; lower diameter 23 cm

Thickness of material: 2 cm (average)

(After Mengoli (1989))

Material Calcite (alabaster) or travertine (Müskens (2017))
Condition Mostly complete - reassembled from fragments
Publications

As this is the most complete example of an Egyptian water clock, JE 37525 is widely referred to in passing throughout Egyptological scholarship. For the sake of brevity, this following list includes only work that provides significant detail:

Legrain (1906); Daressy (1915); Sloley (1924, 1931); Pogo (1936b); Chatley (1940); Neugebauer & Parker (1969); Leblanc and Nelson (1976); von Mackensen (1978); Curto (1984); Dorner (1985); Cotterell, Dickson & Kamminga (1989);  Mengoli (1989); Mills & Symons (2000); Müskens (2017)

Content
External registers 3
External upper band of text Not present
External lower band(s) of text Not present
Exterior Astronomical Diagram Yes, AR1 Water clock (Amenhotep III)
Rim Civil month labels around the rim of the vessel, labelling the twelve columns of hour-marks on the interior surface by season and month.
Interior markings Twelve columns of small round holes, each corresponding with a month name on the rim. Below each of these vertical scales is a raised relief symbol of either an anx or a Dd-pillar which alternate around the interior of the vessel.
Other features The astronomical diagram's upper two registers are interrupted by scene of  Amenhotep III offering to Re-Horakhty (the Sun) and Thoth (the Moon).
Notes

This is the earliest surviving example of an ancient Egyptian outflow water clock. Originally discovered in pieces in Karnak, it has been restored and is on display in Cairo. The incised decoration has remnants of inlay in semi-precious stones.

See also the entry in: Schomberg, A., Berlin Waterclock Project, ID 15 Karnak, 2019, Edition Topoi, DOI: 10.17171/2-10-7. (Berlin cast of this object is ID 1.)

Images

The majority of images found online (by Googling for "Karnak clepsydra" or similar) are of replicas or reconstructions. The Global Egyptian Museum website has one photo here accompanying a record here.