This was an understatement; "at least as good as a cheap chinese starter instrument". It's way, way, WAY better! You should never remove the finish on old valuable instruments. The soul of the instrument is the finish. The history is wiped away...
Well, the damage is done. If I were you I would put spirit varnish on it with a fine brush. You only need 4-5 layers with some wet sanding in between for a nice and thin finish. Easy to do and good for the tone.
Sorry, missed that you bought it already sanded down! I was too upset :-)
Spruce is the hardest wood to stain. The stain will always be more or less blotchy. I have had the best result using water or spirit based stain on raw wood, really wet saturating the spruce with the stain. Using a piece of paper towel to get it on the wood quick and plenty. That way the color will be pretty even. Then clear spirit varnish on top.
The other way is to use very light colored spirit varnish in many coats and build up an even color that way. Painting each coat with the brush in different directions. May take 10-20 coats to get a full color and you can't do any mistakes on the way. No or very light sanding between layers to keep the color even. After a couple of finishing clear coats, you can wet sand to get it smooth without sanding away the color. The good thing is if you do make a mistake, the varnish can always be removed with spirit for another go.
I use 600 paper to smooth the varnish every other clear coat layer. The last shiny layer of clear spirit varnish can be deglossed with the finest steel wool followed with some elbow grease using a cotton or even better a linen cloth. The varnish will need a week or two to harden, when it's dry enough you can get a better shine using the cloth.
I buy it from www.hammerl.com. But there are recipes on the net, in the old days every builder made his own varnish.
Gibson mandolins from that time period were often "Sheraton Brown." If you google "Sheraton Brown stain" you will find a number of suggestions as to how to replicate that color.
Didn't mean to mislead you. Most of the information about Sheraton Brown involves people trying to match the color, and that presumes that you have something to match. Are your back and sides the original color? If not, do you have access to a mandolin with an original finish? If the back and sides are original, there was a comment posted that the birch back and sides were darker than the top, but the color would still get you into the ballpark.
I wonder if anyone has ever taken an instrument into Home Depot. They have a color analyzer that is remarkably good at matching paint colors. I would be willing to give it a try with my 1921 Sheraton brown A-2.
Since it is sanded back to bare wood you could do anything you like. And as you are planning to gift it to your grandchild you could give him/her the choice. She might like to have a nice pink one - although Roger would probably not approve (I am waiting for his reply - probably won't take long).
For discussion - "instruments built long ago were always brown - therefore they must always stay brown, and all instruments built today must also be brown."