Silver carries a higher premium when you buy and a wider margin when you sell it back, compared to gold. The main reason is bulk.
For the same dollar value, silver takes up far more space than gold. Many times the volume and weight. That makes it more expensive to store, move, and insure, and those costs are built into both the price you pay and the price we buy it back at. Gold packs a lot of value into a small, easy-to-handle form, so its costs are lower and its spread is tighter.
Platinum's spread is also higher than gold's, but for a different reason. The platinum market is much smaller and less liquid, so there's more risk in holding it, and that's reflected in the margin.
The exact spread depends on the specific product, its size, and market conditions at the time. For current figures, see our live prices and buyback estimator.
Disclaimer: The above is not financial advice.