Copper toner is a very popular and effective way of getting brown to red-brown tones. Your bottle is small, so it probably doesn't make much, maybe 500 ml (read the instructions on the bottle). The components of copper toners are long lived - copper sulfate, citrate, potassium ferricyanide, maybe ammonium carbonate, maybe something else - so the old bottle may still be good. Copper toner is a direct toner, somewhat related to the iron blue toners. The image is copper ferrocyanide (I think), which is long lasting but not indefinitely stable.