In a message dated 98-07-01 12:17:30 EDT, you write: << (1) I have some Au foil pieces that were conventionally polished which have silicon carbide grit embedded in them that I would like to dissolve away. Having never actually done this, but sort of familiar with the chemistry required, I do not envy you your job! So, saying, it may take successive treatments in dilute, hot Potassium Hydroxide, and then 50% Nitric Acid, at room Temperature. The KOH gets rid of the Silicon, the Nitric takes care of the carbide. Rinse between each step, and afterwards, and repeat, as much as is necessary. Wow, what a problem. (2) These samples were also chemically polished with an etchant composed of 10% potassium cyanide (KCN) and 10% Ammonium persulfate in water. I was wondering if this solution would leave any residues on the surface....Would a 50% hydrochloric acid, 50% Nitric Acid (aquaregia) etch be better? >> As a contributor to Technet who is known for his casualness with chemicals, all I can say is that I do hope you were not downwind from the KCN/Ammonium Persulfate treatment, there could be a couple of animals with a permenant disability, that resembles death... Neither system should give you residues. Either system will dissolve gold from the surface. Aqua Regia, which formally is 66-75% HCl, with the remaining being Nitric is the "safer", but still to be treated with a lot of respect. The aqua regia is a faster etch. Either system is overkill. Consider just a dilute KCN solution, this should likely be enough, unless you have gotten the surface REAL contaminated. Rudy Sedlak RD Chemical Company ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################