It's just pure rng. Took me like 20 weapons and armour forged to just get 1 shader. You're using the right weapons so nothing wrong there. Just pray for good rng. Also use the thing from Ada-1 that lets you get a piece of armour after every forge since that also has the chance to drop with the shader iirc. Good luck on your blacksmith.
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Had several clan members stuck on the same thing for blacksmith, done hundreds of forges, its rng whether you get the shader yes but it wont drop if you not in the right forge with the right weapons
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but he is using the right weapons.. pulse and bow. Hope he's in the right forge though.