I am in need of tips/help/suggestions for tig welding copper. It is 11000 copper and I need to try to weld it so there are no signs of solder. It is .090 thick and I hope to fuse the edges together without filler so the joint is as hidden as possible.
I think you can fuse this directly, but you may have weld quality issues if the material isn't dead clean. Pure copper fuses well. Copper filler is available and not that expensive, and will improve the joint quality. A strip of the material cut from the edge will work if the material fuses well and you need a little filler. Deoxidised rod alo works well, abd as a last resort, electrical wire. Electrical wire may have significant percentages of alloy materials to improve one or another characteristic making it less than ideal as a filler metal.
This isn't so thin that you are likely to have major problems, but if needed, an aluminum backer bar behind a joint will help, as will run a lottle hot and fast to reduce the total heat input.