Arsenic-based pesticide residues have been detected on Arizona State Museum’s (ASM) Diné (Navajo) textile collection using a handheld portable X-ray (pXRF) spectrometer. The removal of this toxic pesticide from historic textiles in museums and collections is necessary to reduce potential health risks to Native American communities, museum professionals, and visitors to these cultural institutions. A leader in engineering innovative pesticide removal methods, ASM received federal funding support to continue essential research in removing heavy metal pesticides from cultural property. The research objective was divided into three interconnected stages: (1) calibrate the pXRF instrument for arsenic contaminated cotton and wool textiles; (2) engineer a textile conservation aqueous washing treatment to remove arsenic from wool textiles; (3) demonstrate the aqueous washing treatment method on actual Navajo textiles known to have arsenic-based pesticide residues. The calibration process consisted of a dipping method to produce known homogenous arsenic cotton and wool test samples saturated with solutions of 100, 500, 1000, 2500, and 5000 parts per million (ppm). A linear correlation between observed pXRF test readings and formulated arsenic solutions corroborated the instruments range of detection for arsenic on specific textile materials. The calibration confirms that the pXRF is suitable instrument to measure the removal of arsenic from wool textiles. Wool test samples treated with solutions of an arsenic concentration of 1000ppm were used to develop an optimal aqueous washing treatment exploring the effects of time, temperature, agitation, and pH conditions to efficiently remove arsenic while minimizing damage to the structure and properties of the textile. Each conditional effect removed a certain percentage of arsenic, although the most efficient aqueous washing treatment consisted of submerging a wool textile in deionized water at room temperature for ten minutes with the greatest level of agitation within reason to minimize damage the textile. The final stage of the research applied the aqueous washing guidelines formulated from experimental research on three historic ASM Navajo textiles. Two textiles contained low arsenic concentrations (<100ppm), and one tested with a high arsenic concentration (~1000ppm). The aqueous washing treatment resulted in minimal change for low arsenic concentration textiles, and a 96% removal of arsenic on a high arsenic concentration textile. The preliminary success of removing arsenic-based pesticide residues from historic Navajo textiles greatly impacts the future management of historic textile collections, and also raises questions to further refine the research methodology or pursue alternative related research such as engineering a closed circulating arsenic removal system to limit the quantity of toxic water.