samples was used to determine the spall threshold of the PDMS oils. Poly(methyl methacrylate) (PMMA) or aluminum (Al 6061) flyer plates, held by a sabot, were launched from a 64 mm-bore single-stage gas gun, and impacted the liquid target assembly. A magnet was embedded in the sabot in order to monitor the impact velocity of the flyer plate using a series of magnetic coil gauges located at the end of the projectile launch tube. The front face of the target assembly consisted of a 3-mm-thick Polycarbonate driver plate which transmitted the shock wave into the test liquid upon impact. The liquid was contained within an aluminum ring which had fill ports through which the liquid was injected via Luer-Lok fittings. Prior to being injected in the capsule, the oils were degassed under vacuum (approximately 100 Pa) until free bubbles no longer appeared. The rear surface of the liquid was held in place by a 51-$\upmu$m-thick aluminized polyester sheet (Mylar), which formed a free surface through which the incident shock wave reflected to place the sample in tension. Although there was a slight impedance mismatch between the liquid sample and the Mylar, the short acoustic travel time across the film (on 