GST classification: pickling and soldering preparations are taxable and attract the applicable GST rate under scheduled provisions. Pickling preparations for metal surfaces, fluxes and other auxiliary preparations for soldering, brazing or welding, soldering, brazing or welding powders and pastes, and preparations used as cores or coatings for welding electrodes or rods are classified under Schedule 3 and attract GST at 18% through the transitional period ending 21-09-2025.