"Why has the fingerboard on my violin dropped?" — I was asked this question just yesterday. The answer is simple: this is how a violin reacts to low relative humidity.
I always advise paying close attention to relative humidity levels, especially during the autumn-winter heating season. Stringed instruments are extremely sensitive to moisture changes. The most comfortable environment for a violin, guitar, viola, or cello is 50-55% relative humidity. It is highly recommended to ensure humidity never drops below 40% or rises above 60%.
Any instrument repairer will tell you that their workload spikes during the heating season. Workshops fill up with instruments suffering from dropped fingerboards, high string action, or severe cracks in the soundboards. The cause is always the same — dry air.
There is a common myth that only instruments made of insufficiently seasoned wood are sensitive. This is untrue. Any high-quality wooden instrument, regardless of age, is vulnerable. For instance, in the Stradivari Museum in Cremona, violins are kept in airtight cases strictly at 50-55% humidity. Cheaper plywood instruments or old violins with many internal patches (a "shell" of glue and cleats) are less reactive, but they lack superior tonal qualities.
My Personal Experience:
When the central heating was turned on in my apartment, the humidity plummeted to 20%. A room humidifier running 24/7 barely maintained 40% in just one room until I covered the scorching radiators with blankets to reduce heat output. Only then did the levels stabilize at a healthy 45-50%.
If managing room humidifiers is too troublesome, there is a simpler solution: the humidifier (Dampit). This is a perforated rubber tube with a sponge inside. The moistened Dampit is placed inside the violin's f-hole or the guitar's soundhole, and then the instrument must be kept in its case. This creates a safe microclimate inside the case. Remember: using such a device outside the case provides very little benefit.