Chipping vs Gorthor Brown

How close are they?

ΔE 6.4, close: similar, with a visible difference side by side. Gorthor Brown is a little lighter, more saturated than Chipping.

Can I use Gorthor Brown instead of Chipping?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Gorthor Brown is a little lighter, more saturated than Chipping.

Can I use Chipping instead of Gorthor Brown?

The same difference applies the other way round: Chipping is a little darker, more muted.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.