i’m fairly new to anodizing niobium and only use the techique as called for with a project. I don’t do this every day as you likely do in your shop. Thus, my TSP and etching solutions may be ”older” than yours at times. I can always make up fresh TSP solution in small quantities and ensure I’m always using fresh solution, but the etchant is more problematic. The way it is packaged I have to make up the whole 1/2 gallon of the 2X concentrate all at one time. (I would make smaller lots if I could divide the dry powder accurately, better yet buy it in smaller units.) I then make up only 1 cup of the 1:1 dilution for a hot etch. After use I always decant it into a heavy polystyrene (?) lidded container for reuse later. I toss this diluted solution if I notice any color tint. Sorry for the long intro ... Because my use is so limited at times, these soultions tend to ”age in place”. Are there any tell-tales to look out for as an early indicator that it is time to use fresher reagents, or explain what I’m seeing when things go differently than expected? Thanks, Rick https://www.reactivemetals.com
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