Serial Number & Marking Reference

Overview of the Marking System

Mathmos — trading under the name Crestworth until approximately 1992 — applied a variety of base stamps, mould codes, and batch identifiers to their lava lamp units across different production eras. These markings were not applied with the uniform rigour of a serialised manufacturing system; rather, they evolved incrementally in response to regulatory requirements, tooling changes, and market conditions. It should be noted that the absence of a particular stamp does not, by itself, indicate inauthenticity, as several early production runs and transitional-period units left the factory with incomplete or partially legible markings.

The primary reference points for dating and authentication purposes are: the base stamp configuration, the country-of-origin legend, the electrical rating text, and where present, any mould cavity numbers impressed into the underside of the cap or the interior rim of the base.

Base Stamps by Production Era

Crestworth Period (c. 1963–1992)

Units produced under the Crestworth name typically bear a base stamp reading “Crestworth Ltd, Poole, England”, sometimes abbreviated or partially omitted on earlier moulds. The earliest documented examples, consistent with production circa 1963–1967, tend to show shallower embossing and a more compressed font, a characteristic that is observable when the base is examined under raking light. By the mid-1970s, the stamp block had been standardised and deepened, producing a more legible impression.

Electrical rating text during this period generally reads “240V ~ 40W” on UK-market units, with the tilde symbol distinguishing alternating-current ratings. Export variants destined for North American markets are known to bear “120V” designations and were fitted with different lamp holders; these units are discussed further in the Mathmos Model Catalogue.

Mould cavity numbers, where present, appear as single- or double-digit numerals impressed near the outer edge of the base underside. These are manufacturing identifiers rather than serial numbers in the strict sense, and their primary value to collectors lies in correlating matched sets — base and cap from the same mould cavity — which can inform assessments of originality.

Mathmos Period (c. 1992–Present)

Following the rebranding to Mathmos, the base stamp was updated to reflect the new trading name, and the Poole address was retained through much of the 1990s. Further evidence is provided by units from the mid-to-late 1990s, which begin to show the addition of a CE marking, consistent with the requirements of the Low Voltage Directive then being implemented across EU member states. The transition from purely embossed text to a combination of embossed and printed labelling is observable in units from approximately 1994–1998, though this varied by model line.

Cap and Globe Markings

The cap — the metal or plastic closure at the top of the globe — occasionally carries its own set of identifiers, though these are less consistent than base markings. On certain models, a small impressed code is present on the interior rim; this is believed to correspond to tooling batches rather than individual units. Caps were periodically redesigned for aesthetic or manufacturing reasons, and the cap redesigned circa 1971 on the Astro model, for instance, represents a well-documented transitional point that can assist in date-banding a unit.

Glass globe markings are rare and, where observed, consist of small embossed dots or numerals near the base of the globe. These are mould artefacts and carry limited identifying information beyond confirming the glass supplier batch in certain cases.

Using This Reference

The patterns documented here are drawn from auction records, museum collection notes, and contributor submissions as catalogued in the Provenance & Auction Record Notes section. Readers seeking to apply these identifiers in a restoration or acquisition context may also find the guidance on Dating Production Runs by Physical Markings and Identifying Authentic Mathmos Models directly relevant, as those pages address methodology as well as the markings themselves.