Empty and half used tins of paint cannot be recycled through the standard household waste curb collections. Unused Paint and varnish or empty tins with residue of chemicals in cannot be put in general waste bins or recycling bins.
It is quite a complex process and needs to be handled by professional licensed companies.
Part used tins of paint can often be recycled by passing on to a paint collecting charity but the paint is used rather than recycled. It’s often donated to people who need it but also used for community programs.
If you do not have a curb collection in your local area or find a paint collecting charity then as a last resort unused, part used and empty tins of paint can be taken to the dump. Most local household waste recycling sites can collect and process old paint but be sure to contact the tip near you for confirmation what paint they accept for recycling.