The layer of gold is relatively thin on GF sheet or wire. 1/20th of the total weight is 14Kt gold. Any abrasive or corrosive methods may go right through the gold layer. Very fine steel wool, a very fine brass bristle brush will give you a matte finish, but you have to apply it very lightly. If you are fabricating and polishing on a buffer do NOT use any tripoli or other fast cutting compound.
Gold Filled is a wonderful "compromise" product but it does require substantially different handling than does sterling.
John at Monsterslayer had a good post about working with GF in the old forums. I'll see if I can track it down in the archives.
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