How do you clean old rings?

Use warm water and a soft toothbrush for most rings. Avoid soaking anything from the Georgian period, as water can ruin the foil backing behind the stone. Keep them away from ultrasonic cleaners. The vibrations can loosen old settings and damage stones with internal flaws.

I saw a ring with a yellow gold band but the part holding the stones is white, did someone repair it badly in the past or was it actually made that way?

Makers deliberately used white metals near the stones. A yellow setting casts a warm tint into the diamond, making it look off-colour. Silver was standard for the top sections before platinum became common. It keeps the diamond looking bright, while the gold shank provides strength.

Can old rings be resized?

Most plain bands are straightforward to resize. A jeweller will add or remove metal at the back of the shank. Eternity bands are much harder to alter.

I was reading online about old cut diamonds and someone said they sparkle less than modern ones because of how they were made, is that actually true for antique pieces?

They sparkle differently. Modern brilliant cuts are engineered to reflect light back in precise flashes. Old cuts have fewer, larger facets that draw the eye deeper into the stone. The effect is a softer, broader flash. Many buyers prefer this understated look, especially in dim lighting where the stones were designed to be seen.