This study reports the chemical composition of historical brickworks from Franciscanbuilt church complexes in the Philippines. An old brick sample from the Spanish colonial period church convento at Pagsanjan, Laguna was characterized by atomic absorption spectroscopy (AAS), infrared spectroscopy (IR), thermogravimetric analysis (TGA), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX). Conventional hot plate aqua regia (1:3 HNO3:HCl, v/v) digestion method was employed to extract iron, calcium, and magnesium from the brick sample. The combined AAS and EDX results yielded a percentage composition of iron ranging from 5.48 to 6.62%, calcium ranging from 1.50 to 3.72%, while magnesium ranges from 0.083 to 0.12%, respectively. These amounts were compared to a similar AAS and EDX study made on a historical brick sample from Ilocos Norte. The presence of possible pores on the brick's microstructure was confirmed by SEM. Minerals consisting of hematite, kaolinite, illite, quartz, and calcite were present in the sample, as well as trace amounts of other minerals based on IR peak intensities. Upon heating to about 800⁰C using TGA, the loss of bound water from the sample's internal surface structure and the decomposition of brick minerals and carbonates are evident.

This study demonstrates the feasibility of performing chemical analyses on heritage materials in the Philippines. Four extraction methods were evaluated based on the percentage of iron, calcium and magnesium in a clay brick sample obtained from an old Spanish colonial period church at Ilocos Norte. Aqua regia (1:3 HNO3:HCl, v/v) solvent was used to extract these elements by conventional hot plate digestion. The extraction methods are: digesting the sample directly with aqua regia (M1), sample pre-digested with NH4Cl and ethyl alcohol prior to the actual digestion (M2) and soaking the sample with aqua regia for 24 hours (M3) and 48 hours (M4) before digestion. Atomic absorption spectroscopy (AAS) was employed to quantify the concentration of the intended elements. The percentage composition of iron ranges from 4.193 to 4.418%, calcium from 0.123 to 0.203%, and magnesium from 2.346 to 2.458%, respectively. Energy-dispersive X-ray spectroscopy (EDX) analysis was done to support the data obtained from AAS. M1 was more effective in extracting calcium from the brick sample, while M2, M3 and M4 were useful for extracting iron and magnesium. Infrared spectroscopy (IR) provided a basic mineralogical composition of the sample, with peaks that were attributed to quartz, kaolinite, calcite, silicates and hematite.

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Spanish Colonial Period brick samples dating to the 19th century from the Municipalities of Liliw and Pagsanjan in Laguna, Philippines was investigated. These samples were obtained from two church structures, a church bell tower from Liliw and a church convent from Pagsanjan. Combined X-ray diffraction (XRD), energy dispersive X-ray fluorescence (EDXRF) and Fourier transform infrared (FTIR) spectroscopy allowed the determination of chemical elements and minerals attributed to clay and sand, such as montmorillonite, quartz, corundum, hematite and calcite. On the basis of these compositions, the possible kilning conditions employed to fire the bricks during manufacture was also proposed. MATLAB™ programme was utilised in this study to interpret the data from XRD and FTIR to rationalise the overlapping peaks in the spectrum. Results show that both brick samples were made of clay material that is non-calcareous with low refractory. The firing was performed in an oxidising atmosphere or an open-air environment at an estimated temperature of between 650°C and 850°C. This preliminary study provides a baseline chemical characterisation data of colonial period bricks in the Philippines which will be useful for future conservation and restoration work not only locally but also within the Southeast Asian region.

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