Penetrol is a great choice for enhancing the application of Spar Varnish, as it improves flow and leveling, making it easier to apply and giving a smoother finish. When using Penetrol with Spar Varnish, a common ratio is about 1 part Penetrol to 3 parts varnish. However, you can adjust this based on your specific application and desired finish. Start with this ratio and test it on a scrap piece of wood to see how it looks before applying it to your sculpture.
As for using Penetrol with Minwax Cherry Stain, it’s generally not recommended because it can interfere with the stain's ability to penetrate the wood. Instead, apply the stain directly to the maple wood and allow it to fully dry before applying the Spar Varnish mixed with Penetrol.
Make sure to work in a well-ventilated area and wear appropriate safety gear. If you're looking for a deeper cherry color, consider applying multiple coats of the stain, allowing each to dry completely before applying the next. Once you're satisfied with the color, proceed with the varnish.
For the best results, consider consulting with a local woodworking professional to get tailored advice specific to your project.
— Assisted answer