Advice for Herco clay humidifier users
 

A sale person at Elderly Instruments told me that since years Elderly has stopped to use these humidifiers inside the case of their guitars, because they noticed that the clay block, when it becomes, dry, actually absords humidity from the guitar and make the instrument even drier. Since then, I modify the Herco humidifiers getting rid of the clay block and replacing it with a normal piece of sponge. It works like a charm under the headstock. I put between the strings a Nomad humidifier.
The Herco modified works well also for my archtops, I use one under the headstock and one close to the body.