@Oliver G @Mesquite Should I go over the handle with a very fine sandpaper before oiling?
Is the handle brand new and never used before?
If it isn't and you've oiled it before then a light rubbing down with fine sandpaper or wire wool won't go amiss.
If it is new and you want to oil it for the first time then prepping it before oiling will go a long way. The way I was taught was to do as follows:
1. First of all if it's been varnished then remove all of that as it'll stop the oil penetrating. Best way I've found is to use a razor blade and scrape it off.
2. Once you've removed all traces of the varnish then take a wet rag and lightly dampen the handle and leave to dry. You don't need to soak the wood, it is literally just a wipe down to dampen the surface. This will bring up loose fibres that might have been pushed into the main wood.
3. Once the handle has dried out feel the handle and if it feels at all rough sand back down with either fine sandpaper or wire wool.
4. Repeat steps 2 and 3 for as many times as it takes until fibres stop rising after it's been dampened down. It should only take 4 or 5 goes at dampening it down before the fibres lay tight and you can dry the handle over either a fire or with an alternative heat source.
5. Oil your handle, leave it for 20-30 minutes then wipe off any excess oil and leave for a day.
6. After a day rub it down with either fine sandpaper or fine wire wool and repeat step 5.
7. You'll want to do step 5 once a day for a week, then once a week for a month then once a month for a year and thereafter once a year maybe twice if you use it heavily.
Word of warning, be very careful with how you dispose of the rags you use to oil the handle. linseed oil on rags have been known to spontaneously combust and cause a fire. KHang them in a well ventilated area or dispose of by burning immediately to prevent any problem this might cause.