*3.3. Mock-Up Study*

Mock-ups were created to allow for more extensive study of the paint alteration as the amount of altered material from the krater was limited. The mock-ups were created in pairs with one terracotta piece acidified using 6N hydrochloric acid and the other without. Each mock-up was painted with a swatch of the pure cadmium orange paint and a swatch of the cadmium orange paint mixed with the Titan Buff, mimicking the conservation treatment.

Initial mock-ups were designed to recreate the conditions which are assumed to have contributed to the formation of the efflorescence observed in 2004. One mock-up pair was sealed in a bag with a small volume of acetic acid, approximately 2 mL, to recreate the proposed scenario which caused the formation of the calclacite efflorescence on the krater. White efflorescence formed on the acidified mock-up after three days. The efflorescence was sampled, analyzed by FTIR and identified as calclacite (Figure 5). No efflorescence was observed on the non-acidified mock-up.

**Figure 5.** FTIR results for efflorescence formed on (**a**) a mock-up treated with hydrochloric acid and exposed to acetic acid, compared with (**b**) the efflorescence that formed on the krater whilst on loan in 2004 and (**c**) a reference spectrum for calclacite from the IRUG database.

Next, a series of mock-ups were created to study the effects of both chloride ions and light on the alteration of the pigment, aiming to investigate whether display conditions had contributed to the alteration. Mock-up pairs (acidified and non-acidified), were placed in bright natural light (1 and 2), non-direct light (3 and 4) and in the dark (5 and 6). The mock-ups in direct light received direct natural light through a window which filters out the majority of UV radiation. Those placed in indirect light were sheltered from direct natural light, mimicking the closest scenario to the display conditions of the object. The mock-ups which received no light were kept in a closed draw.

During the first three months of exposure, mock-ups in direct light received approximately 9 h of natural daylight per day. The amount of light these mock-ups received during daylight hours varied between 207–2624 footcandles, the equivalent of approximately 2140–28,400 Lux, with the measured UV content of the light varying between 5.7–14.4 mW/Lumen (determined using an ELSEC 765 Environmental Monitor). The lower values are associated with overcast, cloudy days and the higher values with bright, sunny days. The amount of light received by the mock-ups in indirect light during the same time frame remained below 10 footcandles (108 Lux) and UV measurements were consistently zero.

The acidified mock-ups in direct and indirect light (mock-ups 2 and 4, respectively) began to noticeably alter within one month with the cadmium orange darkening to brown and the cadmium orange/Titan Buff mixture changing to grey, matching the observed alteration on the krater. The acidified mock-up placed in the dark (mock-up 6) displayed no visible change after one year and no change was seen on the non-acidified mock-ups at any light level. Figure 6 shows the mock-ups after one year.

**Figure 6.** Mock-ups created to investigate the alteration of cadmium orange pictured after one year of exposure to direct light (mock-ups 1 and 2, left), indirect light (mock-ups 3 and 4, center) and no light (mock-ups 5 and 6, right). The pieces in the top row were not acidified prior to painting. Each piece of terracotta is painted with a swatch of cadmium orange/Titan Buff on the top half and cadmium orange on the bottom half.

The mock-ups used for this study were treated with 6N hydrochloric acid to produce a quick reaction. A mock-up treated with 1N hydrochloric acid was created for comparison with the more harshly acidified samples. The same alteration was observed on the mock-up acidified with 1N hydrochloric acid, albeit occurring at a reduced rate in comparison to the 6N counterpart taking at least three months for any noticeable alteration to occur.
