This can often be caused when the Specific Gravity of the solution exceeds 1.45. When Etching Ferrous Metal Plates the specific gravity of the solution should be 1.38 ‐1.42 . Allow the Pump of the spray Etching machine to run for 3-4 minutes before taking any measurements. Using a Hydrometer that covers the range 1.25-1.5 measure the Specific Gravity. If the Specific Gravity is found to exceed 1.45 dilute the solution with water to specific Gravity of 1.42. Also check the acidity of the solution detailed earlier in the FAQ list.