If the varnish is difficult to remove use the chemical procedure using
standard Nitromors paint stripper, but please use with extreme care because if incorrectly used you could end up with a delaminating problem. No matter which method is used proceed at a slow pace. Many fine rods have been destroyed by hobbyists in a hurry to get the job done.
When the majority of varnish is removed, sand the blank very lightly (little pressure is used) with 600 grit (wet and dry) abrasive paper working one flat of the rod at a time. Again, take care not to remove more than is necessary and try not to round the edges of the hexagon shape. It helps if the abrasive paper is glued to a flat stick, something like a wooden ruler is ideal for this.
Check the rod is clean under a strong light. If it isn't clean sand again.
When the blank is clean polish it with 0000 wire wool working in the direction of the rod.
Retain all the original whippings and guides, you will need the whippings to closely match the thread colour.