What etchant have you used? Usually the etchant is water based acid mixture (Marble?), so just rinse it off directly after etching with water, rinse it with alcohol and blow-dry to have it clean. Should be OK than. If you have some residuals, maybe you used come color etchant that leaves oxide layers?

Yes Zhumei... the SS 316 surface must be cleaned after etching to reach a neutral, dry state to perform the next measurements. There are some standard procedures for such purpose. The specimens may be rinsed with water and kept over silica gel for one hour as the simplest cleaning procedure..

I would suggest cleaning the surface after etching. In practices, I've used for metallography I generally etch with Oxalic or another suitable reagent then clean with alcohol and acetone. A scratch-free swab can be suitable for removing the bulk of the residue.

If you are concerned about damaging your sample surface you can try sonicating it as well although care should always be taken when sonicating in any volume of organic solvent since there are inherent hazards involved. If you are not concerned about corrosion products or other surface layers I have used a dilute Alconox (laboratory detergent) mixed with a small amount of corrosion inhibitor to remove any residue followed by an organic rinse (acetone and methanol or iso-propanol)