WELD LAKE PREPARATION Jo Kirby and Catherine Higgitt National Gallery, London May 2005 Eu-ARTECH organic project.

WELD LAKE PREPARATION

Jo Kirby and Catherine Higgitt

National Gallery, London

May 2005

Eu-ARTECH organic project

Reseda luteola L.

English weld

French gaude

Dutch wouw

German Wau

Italian reseda

Recipes fell into 3 broad categories

1. Extraction of dyestuff with limewater solution, then alum (+chalk) added to precipitate lake- Use Boltz von Rufach 1549

2. Aqueous extraction of dyestuff, then alum and chalk (or other Ca salt/lead white) added to precipitate lake- Use 15th C Sienese/Bolognese recipe for arzica

3. Alkali added to aqueous solution of dye (or weld boiled in alkali), then alum added to ppte- Use Dossie, 1758 as example of this type

Recipes – substrates

1. Boltz von Rufach 1549 (lime water; alum/chalk)

- Ca, Al, O: Hydrated alumina/chalk/calcium sulphate

2. 15th C Sienese/Bolognese (alum/chalk)- Ca, (Al): Chalk (trace of hydrated alumina?)

3. Dossie, 1758 (alkali, alum)- Al, O: Hydrated alumina

Recipes

• Most of the examples of yellow lakes we encounter in paintings are pre-1800 so deliberately avoided 19th C recipes

• Steps in manufacture– Extraction/boiling– Removal of plant material – Precipitation of lake– Filtration and washing of lake– Drying and grinding of products

Dry weld – broken up before use

Extraction

time

Filtering extract

Filtrate

Precipitation – Lake 3 –(i) addition of K2CO3

Precipitation – Lake 3 – (ii) addition of potash

alum

Precipitation – Lake 1 –

addition of chalk/alum mix

Precipitation – Lake 1

Precipitation – Lakes 2 and 3 – settling out

Filtering lake

Filtering and washing lake

eventually

Filtering and drying lake

Grinding Lake 3