Furniture, Wood and Cabinetry Finishing - Finish wooden rocker w/o removing patina

My Mom has an antique wooden rocking chair that belonged to my great-grandma. I washed the chair with Murphy's Oil Soap. I followed some of the other advice I've read here in trying to figure out what the finish is. I gently rubbed a small area with a rag dampened with denatured alcohol. It started to take what is left of the finish off along with some of the dark stain. Does this mean the finish is shellac? I do not want to strip the chair of it's old patina, yet I want to do something that will protect the wood so we can use it occasionally. I've read & heard that if I strip the chair of its finish, I would ruin it's value. What should I do now to protect the chair without ruining it? Should I put a coat of new shellac right over what's left of the old finish? How glossy will it be? Should I apply more than one coat? What do I do in between coats? What is available in shellac? Are there different levels of gloss available? I am new at this. Any and all suggestions and advice is greatly appreciated.

Thanks!
Alan

It could just be furniture wax. If you scrape it with your fingernail and it comes off, it's probably been waxed, and the "patina" is actually dirty wax, and is probably NOT stain. So that's a possibility. Shellac is also a form of wax, but it's usually hard enough to resist fingernail scratching. If you apply more shellac without cleaning the chair, you'll trap the dirt between coats. I guess if that's what you want...

I scraped the finish with my fingernail and it DID NOT come off. I DID clean the chair with Murphy's Oil Soap. Since my fingernail did not scratch the finish, does that mean it is shellac? What should I do next?