Laser Cleaning of Excavated Greco-Roman Glass: Removal of Burial Encrustation and Corrosion Products

Abstract

The potential of using laser-assisted cleaning for the removal of burial encrustation and corrosion products on Egyptian glass fragments (from between 332 bce and 395 ce) excavated from Sinai (Egypt) using a 10 nanosecond Q-switched Nd:YAG laser operating at 1064 nm has been assessed. A series of complementary analytical techniques including microscopy, Fourier transform infrared spectroscopy, static secondary ion mass spectrometry with a focused ion beam and scanning electron microscopy coupled with an energy-dispersive X-ray spectrometer were employed to characterize the glass deterioration phenomena. Following the optimization of laser cleaning parameters, results suggest that laser cleaning successfully removes both the burial encrustation and degradation products, without damage to the underlying glass substrate.ÖZET Mısır Sinai'deki kazılarda bulunan antik cam parçaları üzerindeki korozyon ve gömü ortamı yüzünden oluşan kabuklanmaları temizlemek için lazer yöntemi (10 nanosaniye, Q-switched Nd:YAG lazer, 1064 nm) denenmiştir. Camın bozulma sebeplerini tanımlamak için, bir çok analitik teknik (mikroskopi, Fourier-Dönüşümlü Kızıl Ötesi Spektroskopi, Odaklanmış iyon ışınlı statik ikincil iyon kütle spektrometresi, ve enerji dağıtıcı X-ray spektrometresi ile birleştirilmiş tarama elektron mikroskobu) kullanılmıştır. Lazerle temizleme parametrelerinin uygunlaştırma yöntemlerini takiben alınan sonuçlar lazer tekniğinin, gömü ortamı sebebiyle oluşan kabuklanmayı ve bozulmayı, camın kendisine zarar vermeden başarılı bir şekilde temizlediğini kanıtlamıştır.

Evaluation of Cleaning Soiled Deposits and Crusts from Archaeological Glass Using Laser Treatment with Ag/Au Nanoparticles

“…Silver and gold nanoparticles were applied to the surface of the samples in the form of a solution using a swap and left to dry, and then a laser was applied. Laser cleaning was performed using the Nd: YAG laser emitting at 1064nm and pulse duration in the range 8-10 ns, repetition rate 10 Hz, energy 50 mJ/pulse, and fluence of 0.8 J.cm -2 with five pulses based on the good outcome of the previous studies conducted on the archaeological glass [4,33].…”

“…Choosing the methods for cleaning glass artifacts relies on the extraneous substances present on the surface to be removed, which vary, starting from the soiled deposits that accumulate on the surfaces of the glass artifacts buried in the soil and even the deterioration products that form and stick tightly to the glass surfaces as a result of the physiochemical interactions between the glass and the surrounding environment [4].…”

“…In the previous works, Nd: YAG laser was the best choice for artifact glass cleaning with thick layers of corrosion [4,33]. The excimer laser successfully cleaned stained glass [34,35], characterized by its transparency.…”

“…The color of artifact glass may be changed due to the strong absorbance of UV light due to photo-oxidation of manganese dioxide in the glass. Therefore, the YAG laser, which emits photons at 1064 nm, is preferred for removing encrustation corrosion on the glass extracted from excavations [4,36].…”

Archaeological glass conservation and restoration intervention materials – a literature review

“…São ainda referidos a utilização de pincel com motor, picareta de madeira, escovas ou espátula que são potencialmente métodos mais invasivos de limpeza, já que a sua utilização de forma incorreta poderá contribuir para maior dano na superfície do vidro, podendo, no mínimo, provocar abrasão. Em 2010, Elnaggar e coautores [32], sugeriram o uso de laser para limpeza, já que este não interfere mecanicamente com a superfície do vidro, alegando que a limpeza mecânica pode criar fissuras e abrasão e que a limpeza por via húmida com ácido etilenodiamina tetra-acético (EDTA) pode provocar danos irreversíveis ao alterar a estrutura química do vidro (este processo será descrito mais à frente). Os autores afirmam que o sucesso deste método se relaciona com o comprimento de onda emitido, em que, tendencialmente, os produtos presentes nas incrustações absorvem a radiação, mas não o substrato (vidro).…”