The giant glass plates of the Alinari Archives Restoration and enhancement of the collection

We are pleased to present a project on the preservation and promotion of the collection of 170 oversized glass plates from the Alinari Archives. Although the existence of these so-called “imperial” format plates was known, these phototypes - which have been preserved for over a century at the Alinari company in Largo Alinari, Florence - have never been the subject of a systematic study.

The collection has been carefully restored, cataloged, and digitized - using PNRR funds - and is now available for consultation for the first time.

Introduction

The Alinari Archives preserve an extraordinary corpus of 170 large-format glass photographic plates dating from approximately 1860 to 1920. The images depict works of art, architecture, and panoramas, primarily of Florence and Rome, but also include views of Venice and Tuscan subjects. These materials are distinguished by their exceptionally large format - with examples exceeding 110 cm per side - their high photographic quality, and their rarity, constituting a unique heritage.

Historical sources trace the earliest examples of this rare and extraordinary production back to the experimental work of Giuseppe Alinari (1836–1890).

Diego Martelli, in his 1890 text In memoria dei Fratelli Alinari, written on the occasion of Giuseppe Alinari's death, also mentions this exceptional production. He recalls that the Alinari brothers, after the death of founder Leopoldo in 1865, led the company "always at the forefront of every advance," and "reproductions of the most sought-after paintings in our Galleries were produced, in dimensions never before attempted, or even conceived, since it involved preparing plates measuring as much as 1.15 meters high and 85 meters wide."

The creation of these large negatives fulfilled the goal of obtaining contact prints faithful to the dimensions of the originals, as evidenced by the 1899 photograph of the washing tanks in the Florentine factory, and of standing out at international exhibitions. The dimensions of the negatives were closely linked to the available printing techniques. Before the widespread use of enlargers, contact printing required a direct correspondence between the size of the negative and that of the final print. Producing very large-format negatives was therefore the only viable way to obtain large-scale positives capable of exerting a strong visual impact. These negatives could be made directly during the shooting phase using large studio cameras, or produced by rephotographing smaller-format positives onto large plates.

Technical features

Observation of the technical characteristics and study of the stratigraphic components of the plates, conducted during the restoration and digitization campaign, proved essential for a thorough understanding of these impressive photographic artifacts; the unique dimensional characteristics and considerable weight of the supports made the conservation activities particularly complex.

The corpus of oversized plates consists of 170 phototypes on glass supports, measuring between 59.1 x 59.1 cm and 114 x 84.5 cm, with plate thicknesses ranging from 0.3 cm to 1.1 cm. The collection comprises 156 gelatin silver glass plate negatives, 13 wet collodion glass plate negatives, one negative and one positive on glass plate with pigment-based photographic image, and one silver gelatin film positive.

The material is also particularly significant from the perspective of post-production practices, as it preserves numerous manual interventions aimed at correcting and optimizing the image; in this context, annotations and technical instructions have sometimes been found on the paper masks applied to the plates, providing valuable evidence of the operational procedures adopted in the image production process.

Restoration intervention

Consultation and study of the material were hampered by heavy dust accumulation, breakage of some plates, and preservation systems inadequate for objects of this size. The plates had been stored wrapped in paper unsuitable for long-term conservation.

The restoration project aimed to stabilize the material by consolidating the supports and reattaching detached emulsions, with the goal of limiting or eliminating existing and potential causes of degradation, and improving image readability in preparation for digitization.

The plates appeared extensively dirty and dusty and showed numerous physical damages attributable to rubbing, handling, and use. However, the most significant issues were chemical in nature. Among the alterations observed were stains, fingerprints, yellowing of the binder, "silver mirroring" phenomena, and alterations to the glass support. In some cases, there were also traces of microfungal attack and small gaps in the paper masks attributable to entomological attack. The paper masks showed signs of aging and structural weakening.

Dry and wet cleaning were performed, along with consolidation of the emulsion layer and of paper masks, emulsion re-adhesion, assembly of small fragments, and reinforcement of the lesions with sutures.

The exceptional size of the photographic materials required the design of custom-made conservation folders. The plates were then placed vertically in special containers, while the broken ones were subjected to a specific conservation assembly and stored horizontally.

Non-invasive diagnostic techniques

A photographic survey was performed on a selection of plates using multispectral imaging techniques, with both grazing and reflected light across visible, ultraviolet, and infrared bands.

Diagnostic imaging is a set of non-invasive techniques that use the captured image as a source of data for both documentation and critical assessment of the artifact, allowing for an extensive analysis of the studied object. Specifically, these investigations allowed for the analysis of manual interventions, alterations, and degradation phenomena not always visible to the naked eye.

They also made it possible to clearly identify areas affected by finishing and retouching interventions: the infrared light shots highlighted the chippings made on the reproductions of works of art, while the ultraviolet shots allowed for a more precise observation of the progression and distribution of the binders and protective varnishes applied to the surfaces, as well as to detect the treatment of the translucent papers used for masking.

Digitalization and access

The digital acquisitions were performed in transmitted light using the matrix technology, capable of achieving resolutions in the order of billions of pixels and ensuring an exceptional level of detail. This technique, also known as gigapixel imaging, involved dividing the image area into regular portions. The images were then acquired with a camera through multiple shots at very high resolution; the individual frames were subsequently aligned and assembled using software, thus obtaining a continuous and complete representation of the object.

The project was part of the Tuscany Region's cultural heritage digitization plan, made possible thanks to funding from the National Recovery and Resilience Plan (PNRR), Mission 1 – Digitalization, Innovation, Competitiveness, and Culture, Component 3 – Tourism and Culture 4.0 (M1C3), Measure 1 – Cultural Heritage for the Next Generation, Investment 1.1 – Digital Strategies and Platforms for Cultural Heritage, Sub-investment 1.1.5 – Digitalization of the Cultural Heritage.

Following digitization, this group of plates was catalogued by the Foundation using a record sheet updated to comply with ICCD standards (F/MIDF).

The entire corpus can be consulted online on the Foundation's website in the dedicated section, which allows viewing of the images in high resolution.

The Foundation has also developed an educational program for schools: the workshop Discovering Photography in the Age of the Alinari Brothers.

Glass Giants: Restoration and Initial Investigations into the Extra-Large Glass Plates

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Watch the talk "Glass Giants: Restoration and Initial Investigations of the Oversized Glass Plates," part of the series "NEWS FROM THE ARCHIVES 2025," featuring Barbara Cattaneo, Giulia Fraticelli and Eugenia di Rocco. The talk presented the restoration campaign for the 170 oversized glass sheets for the first time.