exterior surfaces of the dovetail 18 exposed by the passage 40 in the masking assembly 10 the masking assembly 10 is also represented in fig2 and 3 as further having a retaining ring 28 to secure the masking shells 12 together the ring 28 preferably forces the mating surfaces of the shells 12 together with sufficient force to close the split line 30 between the shells 12 and prevent entrance of the coating vapors into the cavity 24 for this purpose the retaining ring 28 preferably has a draft angle machined into its surface contacting the masking shells 12 to ease its installation and removal from the masking assembly 10 while locking the ring 28 in place fig2 further shows a sealing material 32 deposited along the interfaces 34 between the masking shells 12 and the blade 14 to further inhibit coating penetration the sealing material 32 may be for example a maskant material of a type used in the prior art as described previously such as a tape putty or bead of slurry suitable materials for the masking shells 12 and retaining ring 28 include metallic and ceramic materials in practice the nickel base superalloy commercially known as inconel 600 has been shown to be a durable and reusable material for both the shells 12 and ring 28 though it is foreseeable that other materials could be used the surfaces of the masking shells 12 and ring 28 that contact other components of the assembly 10 or the blade 14 are preferably machined to ensure an appropriate fit in.