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THE PROCEDURE
The proposed system designates solders based on the difference between the substrate’s solidus temperature and the solder’s liquidus. However, different karat alloy formulas have different solidus temperatures. For this reason, I had to determine a benchmark number that could be used to represent the karat grouping—which became my second major challenge in this project.
Given the wide range of karat alloy formulas from different manufacturers, I realized that as soon as a temperature was identified as a benchmark, some manufacturer would say that temperature did not match the system it currently used. But since no single manufacturer’s set of standards can be adopted as a universal benchmark, I focused on determining a reasonable temperature that could represent a given group of karat alloys.
The first step was to gather accurate solidus and liquidus temperatures of karat gold alloys and solders. Associates in the technology department at Stuller used a differential scanning calorimeter, which measures temperatures and heat flows associated with thermal transitions in a material, to gather this information.
Thermal data was collected from 32 different karat gold alloy combinations to begin building the benchmark number. Single samples of red and green alloys, along with a single 22 karat alloy, were dropped from the reference list because the available samples were too few to be objective, reducing the total alloy combinations to 25. The final reference list included six 10k alloys, 12 14k alloys, and seven 18k alloys. When broken down by color, there were 15 yellow alloys and 10 white alloys.