Celia Leoudi – Revealing Absence

Winnaar Dutch Daylight Student Award 2026
Project type: Research

Revealing Absence

Marble restoration commonly relies on new marble additions or clearly contrasting contemporary materials. New marble restores formal continuity but may obscure the distinction between original and restored fabric, whereasnew materials likesteel, concrete or gypsum remain recognisable but can disrupt the monument’s visual hierarchy. This tension reflects a central conservation principle: replacements should integrate harmoniously while remaining distinguishable from the original fabric (ICOMOS, 1964).

Structural glass offers a third approach, reconstructing missing volumes while retaining the legibility of loss (Barou et al., 2018a, 2018b). Van Nimwegen (2020) explored cast -glass replacement of missing Parthenon column drums, but primarily at a theoreti cal level. This research extended that precedent through experimental material development, optical characterisation, lighting simulation and expert evaluation. The Parthenon’s west colonnade served as a heavily documented reference case rather than an immediate implementation proposal.

Research question
How can cast-glass be developed as a conservation-compatible restoration insert for marble monuments, using light, translucency and materiality to harmonise with the original fabric while preserving the perceptual legibility of absence, authenticity and reversibility? The broader research also examined interface design and reversibility. However, this paper focuses on the material, optical, lighting and perceptual findings most relevant to daylight research.

A research-by-design methodology combined material experimentation, optical characterisation, lighting simulation and expert evaluation.Three batches of kiln-cast soda-lime glass specimens were produced by varying firing schedule, cullet size, placement method, colour recipe and cullet arrangement. Their effects on translucency, colour, veining and casting quality were assessed. Selected specimens were compared with Pentelic marble through illuminance and reflectance spectrophotometry, measuring transmittance, chromatic response, lightness, chroma and gloss.

The measured properties informed ClimateStudio renderings under clear and overcast daylight across seasons and times of day. A night -time scenario approximated the existing Acropolis perimeter lighting using technical information supplied by lighting desig ner Eleftheria Deko (E. Deko, personal communication, 2026).

Material photographs and rendered stimuli were evaluated through a bilingual expert survey involving 37 respondents from architecture, conservation, archaeology, engineering and lighting design. The survey assessed translucency, visual compatibility, visual subordination, preservation of dignity and integrity, the appropriateness of glass and the clarity of the narrative of “revealing absence”. Descriptive statistics and Spearman rank -order correlations were calculated.

Results
The material experiments showed that h igher firing temperatures increased flow and transparency, larger cullet increased light transmission, the flowerpot technique promoted marble -like veining and alternate stacking produced clearer veins than stochastic mixing..

No specimen reproduced Pentelic marble across all criteria, consistent with the objective of distinguishability.Specimen B3T2C1R6 -2-3 provided the most balanced result, combining controlled transmittance ( 1.68%), low chroma ( C = 1.03 *), low gloss ( 2.65 GU ), a relatively warm transmitted -light response and legible internal veining. Its reflective lightness remained lower than that of marble. Compatibility was therefore approached through controlled translucency, colour, gloss and internal structure rather than direct imitation.

The simulations showed that appearance changedsubstantiallywith sky condition, solar direction, season, scale and viewing distance. In daylight, the glass maintained a marble-like visual weight while its translucency preserved material distinguishability. Under night-time artificial illumination, excessive transparency or luminosity risked making the insert visually dominant, demonstrating that material and lighting responses must be calibrated together.

The expert evaluation was cautiously positive. Preservation of the monument ’s dignity and integrity received the strongestoverall rating, while visual compatibility was more contested. Narrative clarity and visual compatibility showed the strongest relationship ( Spearman’s ρ = .832, p < .001 ), indicating that acceptance increased when the intervention was understood as revealing absence rather than imitating marble.

Conclusions and limitations
Translucent cast -glass can develop a marble -like yet distinguishable character when formulation, surface finish and lighting response are considered together. Daylight operated as a design variable governing compatibility, subordination and legibility, while artificial lig hting extended the assessment across the monument’s full visual cycle.

The principal contribution lies in connecting experimental material development and optical measurement with context -specific lighting simulation and expert perception. The results showed that visual compatibility depended not only on numerical resemblance to marble, but also on whether the intervention communicated historical absence meaningfully.

The study remained at feasibility level. Specimens were laboratory -scale, lighting was evaluated through renderings rather than full -scale mock-ups, and the survey represented expert perception. Further research should include larger casts, physical daylight and artificial-light mock-ups, durability testing and lower-risk pilot applications before the approach is considered for highly sensitive monume

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