The most common and most likely answer to this crossword clue is the 6 letter word ARGENT
I've seen this crossword clue in Independent
A
R
G
E
N
T
More clues leading to the result ARGENT
- Tincture cannot be good taken internally
- White border once with no end of geranium
- Instrument lined with lead to reinforce old metal
- Heraldic colour of particular gentleman
- Skill needed to include details in silver on shield?
- Representative having to guard king’s silver
- Broker handling king’s silver
- Silver hair ultimately concealed by a chap
- . Silver ring lost? No great shakes
- Silver transformed garnet
Buddy explains!

The straight part
We know that "old metal" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old metal = argent.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ARGENT mean?
ARGENT noun- The metal silver.
- The white or silver tincture on a coat of arms.
- Whiteness; anything that is white.
- Of silver or silver-coloured.
- : of white or silver tincture on a coat of arms.