The combination of cobalt and iron toner generates violet to blue-violet hues. The degree of toning depends on the dilution of and the duration in the cobalt toner. Shorter toning times only generate a subtle tone in the highlights. Longer toning times also affect the shadows. The subsequent iron-blue toner only reaches those areas that have not yet been fully toned by the cobalt toner. Prepare the working solution of cobalt toner just before you use it. It is only usable for about 60 minutes! All the solutions in the kit combined make up between 2.5 and 5 litres of working solution. The stock solutions have an almost unlimited shelf life. So it makes sense to only prepare the amount you absolutely need. The working solution of the iron-blue toner has a shelf life of several months and can be used until exhausted.