This type of “restoration” is not advised unless the stretcher cannot be salvaged.
In square and rectangular paintings, the stretcher is composed of four wood bars (stretcher bars) over which the canvas is stretched then fastened.
The unpainted portion of the canvas is white, the wood of the stretcher is light in color without any indication of oxidation, and the canvas is fastened to the stretcher with staples.
This is a 17th century painting that appears at such at its front, but may not with a glance to the back, but it has been relined with linen and placed on a new stretcher and fastened with modern staples.
If a painting is on artist board (Masonite) it was produced after 1924, although a Masonite-like artist board was produced as early as 1898 by hot-pressing waste paper.
Older paintings are done in oil paint, which has been used since the 13th century, whereas newer paintings may be done in either oil or acrylic paint, which has been used since the 1950s.
Familiarize yourself with the difference in appearance between old and new oil paintings and between oil and acrylic paintings; oil paintings are more translucent.