a significant advantage to plasma spraying and other techniques involving excess and over sprays which require masking and subsequent machining coatings can be selectively applied to particular inside surfaces as desired for example the inside surface of cylindrical parts may be coated by the process of the invention the data obtained by loss measurements on cylindrical test cavities of copper and iron are shown in fig1 3 the test cylinder dimensions were 1 148 u00b1 0 001 inch o d 0 980 u00b1 0 001 inch i d and 0 800 u00b1 0 001 inch height the cylindrical cavity parts were inserted between plates with hollow ferrules protruding into the cavity in a configuration similar to that used in rf cavities in klystrons and coupled cavity traveling wave tubes the main effect of the ferrules was to lower the cavity resonant frequency from about 9 2 ghz to approximately 7 0 ghz the cylinders when tested prior to coating exhibited q values of 5 390 for copper curve 10 in fig1 and 1 110 for iron curve 12 after coating the copper and iron cylinders each exhibited q values of approximately 210 as shown in fig2 and 3 respectively the q of cavities with kanthal u00ae alloy was higher by more than 50 which proves the superiority of the new coating the change in rf transmission and reflection in an s band coupled cavity circuit section having five cavities is seen by comparing fig4 no loss coating with fig5 loss coating in the middle of the passband at approximately 3 4 ghz the coating increases the transmission loss from 0 55 db to 3.