Annotated Diagrams of Lava Lamp Wax Behaviour
How to Read These Diagrams
Each diagram on this page isolates a specific physical event inside the globe — blob formation, convective cycling, density stratification, or a recognised failure state — and labels the forces, temperatures, and material boundaries involved. Measurements given in annotations correspond to values documented in the reference tables, so the two pages are best read alongside each other. Where a process unfolds in stages, numbered callouts follow the sequence in time rather than by position on the page, which matters most when tracking a blob through a full convective cycle.
Colour conventions are consistent throughout: amber tones represent wax above its melting point, pale yellow represents solid or partially crystallised wax, and blue gradients represent the surrounding fluid at varying temperatures. Arrows indicate direction of net force or movement, not instantaneous velocity.
Blob Formation and Detachment at the Base
At operating temperature, wax at the base exists as a low-viscosity melt pooled against the globe floor. The critical moment is detachment: as the wax pool accumulates heat, individual volumes become buoyant enough to overcome surface adhesion. The annotation here marks the contact angle at the wax–glass boundary, which narrows progressively as the blob neck forms. Detachment occurs when buoyant force exceeds both surface tension and the residual adhesion force at the neck — a threshold that shifts measurably with fluid salinity and wax compound density, both of which are addressed in the density calibration page.
The upward arrows are scaled to indicate relative buoyant force magnitude at three positions: directly above the heat source, at mid-globe height, and near the top. The force diminishes with height as the surrounding fluid warms and its own density decreases, which is why blobs slow and begin to cool before reaching the surface.
Convective Cycling and the Thermal Gradient
The convective cycle depends on a stable vertical temperature gradient: hotter at the base, cooler at the top. Isothermal contour lines in this diagram make that gradient explicit, showing the temperature at which wax crosses from net-buoyant to net-dense. A blob ascending through this gradient is continuously losing heat to the surrounding fluid; once it crosses the neutral buoyancy isotherm, it begins to slow, then descend.
The descent path is annotated separately from the ascent path because they are not symmetrical. Descending wax, now partially crystallising, may route along the globe wall rather than through the centre — a behaviour more pronounced in lamps with convex rather than flat base profiles. This accounts for the characteristic curtaining effect visible in well-calibrated Mathmos units.
Failure State Diagrams
Wax that is incorrectly calibrated, thermally shocked, or chemically degraded produces recognisable failure geometries. Three states are illustrated:
- Floating ceiling wax — a continuous layer of wax that remains at the top of the globe and does not descend. The annotation identifies the density inversion responsible: wax that has permanently shifted below fluid density, often following compound separation.
- Settled floor wax — wax that pools at the base and does not detach. Annotations mark where the buoyant force threshold is no longer reached, typically due to excessive fluid density from evaporation or additive drift.
- Clouding and emulsification — the fluid column shows a milky dispersion. Callouts indicate where surfactant breakdown or wax micro-droplet suspension has disrupted the optical boundary.
Full causal explanations for each of these states are given on the wax failure causes page, with corresponding corrections on the cures and corrections page.
The diagrams here are intended as a visual complement to the analytical content elsewhere on Rewax Guide. Readers working through a specific failure state will find it useful to cross-reference these illustrations with the thermal behaviour page for the underlying physics, and with the reference tables for the numerical values that each annotated measurement refers to.