Brushes for Platinum printing are made by japanese traditional craftsman. Synthetic hair is hand bound with cherry bark band and silk thread in a wooden handle. There are no metallic parts, so you do not have to worry about rust or metallic contamination.
The amount of and length of the nylon bristles gives an optimized application of photosensitive solution allowing for a smaller amount of photosensitive solution. The bristles are especially resistant to chemical deterioration.
This brush uniquely applies a smooth application of emulsion. This is the softer version of this brush and it is used for applying to very thin Japanese washi papers. It can be noticed in the YouTube video of "Platinum printing on Tosa Washi Platinum Paper". The Sku for the soft brushes include an S at the end. The regular brushes are appropriate for western made papers and include an R at the end of the Sku.