Balsa wood is light and soft, at the same time, it is strong for its weight and size to bear the pressure. It is usually used to make model aircraft, and during World War II, it was even used make a real fast-moving bomber plane which was known as the Haviland Mosquito. The balsa wood can be curved and arched easily, but without some specific practices, it may be split or broken when you are trying to shape it. If you want to arch the balsa wood, you can read this article. And you have to prepare some tools for your work: container of appropriate size, warm water, arch template, asking tape, balsa wood and so on.
Make sure the container is large enough to submerge the balsa wood in easily. And then pour ammonia and warm water into the container. Mix the ammonia and warm water. And then fit the balsa wood in the container which is full of the mixture of ammonia and warm water. Leave the balsa wood in the container for at least one hour to make sure it is soaked enough to break down the balsa wood at a cellular level. And then the balsa wood will be more flexible than it used to be.
When the balsa wood is soaked enough, place it on the arch template. Use the masking tape to tape the balsa wood firmly when it has been adjusted into the desired arch. In order to make the bending easier and the finished piece stronger, keep bending the balsa wood.
Finally, we need to wait the balsa to dry. The process of drying is based on humidity and temperature, so if the weather isn't fine, it may cost a few days for waiting the balsa wood to completely dry. Even the wether is good enough, it will need a full day to dry. When the balsa is completely dried, remove it from the template.