Documentation

The DttG database can be queried in two ways:

• Simple query — filter paintings by a single parameter such as colour, city, artist, or institution.
• Advanced query — combine multiple parameters to produce a refined result.

Results of queries are displayed in a tabular format, allowing for easy comparison and analysis of different paintings based on the selected criteria. The results can be exported as a .csv file for further analysis in external software.

Each result links to a full entry with bibliographic references, ground-layer descriptions, and reliability rating. Colour information for each painting is displayed using the standardised DttG colour categories described in the Colour System section below.

If you are new to the database, the Reliability System section explains how to interpret data quality ratings before drawing conclusions from query results.

For more, see the dedicated 'Guide for Using' section on the RKD Study.

In order to build a comprehensive database of Dutch and Flemish ground colours, it was necessary to use "mixed quality data" so that published and unpublished information across institutions with varying degrees of technical research could be presented and queried together. A reliability rating system was developed so that patterns and conclusions could be filtered based on the level of research conducted on the ground layers of individual paintings.

Each painting entry in the DttG database is given a numerical rating from 1 to 4, representing the reliability of that entry's data:

1 Most reliable

Elemental analysis (such as SEM-EDX) has been performed to confirm microscopic cross-section analysis.

2 Microscopic cross-section

Cross-section analysis with light microscopy; no elemental confirmation.

3 Surface analysis

Surface examination by a skilled individual, ideally a paintings conservator with magnification.

4 Written descriptions

Written descriptions form the basis; research methods are unclear.

For more, see: Hall-Aquitania, Moorea. "Common Grounds: The Development, Spread, and Popularity of Coloured Grounds in the Netherlands 1500–1650." University of Amsterdam, 2025, pp. 41-43.

The database uses the terminology system for preparatory layers developed by Maartje Stols-Witlox, in which grounds are defined as preparatory layers covering the entire surface to be painted. Ground layers are numbered from the lowest layer and described qualitatively (e.g. a red first ground and a light brown second ground).

For a detailed definition of preparatory layers and terminology, see: Stols-Witlox, Maartje. A Perfect Ground: Preparatory Layers for Oil Paintings 1550–1900. London: Archetype, 2017, pp. xi–xvi.

For a further explanation of the terminology and systems used specifically for this database, see: Hall-Aquitania, Moorea. "Common Grounds: The Development, Spread, and Popularity of Coloured Grounds in the Netherlands 1500–1650." University of Amsterdam, 2025, pp. 22-25.

The decision not to include images of cross-sections was made early on, due to several reasons including image rights, lack of consistent colour-correction and/or variable instrumentation, limited access to the raw data from previous research, and lack of time to re-photograph available samples at a set standard. It is hoped that it will be possible to address some of these issues in the future to include sample images in the database. For now, the location of available images has been noted wherever possible so that researchers can request access from the relevant source or institution.

1. For chalk layers, the colour given is light yellow (LY) to distinguish from lead white layers (W) and to account for the yellowing of chalk in animal skin glue (and oil).
2. For paintings with more than three ground layers, the full structure is listed as free text but only the top and bottom layers are categorised and described systematically. This allows sorting on the top ground layer colour without expanding the entire system to accommodate the small number of paintings with four or more ground layers.
3. When interpreting ground colour categories from written text where the sample was not accessible, the most reasonable judgement has been made based on the original researcher's description and, where possible, the pigments listed. All faults and inconsistencies are the responsibility of Hall-Aquitania.
4. The most difficult colour categorisation is between red and orange, as this differentiation often relies heavily on the microscopy and photography equipment used. All faults and inconsistencies are the responsibility of Hall-Aquitania.

The DttG database was developed by Paul van Laar in 2022 using the open-source, server-side web framework Django. Django is free and open-source and uses Python. It is used here to browse through the linked DttG SQLite3 database, using querysets of that data to populate HTML templates. The webpages the user requests are generated dynamically with data from the database; any updates made to the database will thus automatically be reflected in the relevant pages as they are requested.

A multi-sheet Excel file was kept as the primary input for the database, to retain ease of use for cultural heritage researchers with varying technical backgrounds. This file is then inserted into the SQLite3 database using a Python script.

The functionality of the database is flexible and can be expanded as desired. At this stage it allows for filtering data on a range of parameters (city of execution, artist, museum, etc.) as well as running complex queries that can be exported in .csv format for analysis in external software.

The code for this project is open source and available on GitHub at https://github.com/TAHPaul/DttG_db. This repository can be used as a starting point or template for similar projects, and includes documentation on the codebase, and import scripts that populate the database.

For further technical detail on the database design and tool workflow, see the accompanying RKD Study article: Designing the DttG database and tool.

For questions about data reuse, corrections, or contributions, please contact Moorea Hall-Aquitania at hall-aquitania@rkd.nl. For submissions, please follow the submission guidelines published in the accompanying RKD Studies article.

If you use data from this database in your research, please cite the database and accompanying RKD Study:

To cite the entire database:

Hall-Aquitania, Moorea, and Paul J.C. van Laar. Down to the Ground Database. RKD Studies. Accessed [Month Day, Year]. https://downtotheground.rkdstudies.nl/

To cite an individual entry:

Hall-Aquitania, Moorea, and Paul J.C. van Laar. "M001: The Fall Of Man." Down to the Ground Database. RKD Studies. Accessed [Month Day, Year]. https://downtotheground.rkdstudies.nl/entry/M001/

Original source citation, where available, are found on individual entry pages and should be cited alongside the database entry.

RKD Study:

Hall-Aquitania, Moorea, and Paul J.C. van Laar. The Down to the Ground Project and Database of Coloured Grounds. RKD Studies (2025): https://dttg.rkdstudies.nl/contents/.