The OED makes it clear that 'gold' is a noun, not an adjective. Thus 'gold' jewellery is jewellery made out of gold.
a. The metal regarded as a valuable possession or employed as a medium of exchange; hence, gold coin; also, in rhetorical use, money in large sums, wealth.
But 'golden' is an adjective and is applied to things which, either practically or metaphorically resemble gold or resemble what gold represents, one of the meanings being :
a. Of the colour of gold; that shines like gold.
However the OED states the primary meaning of 'golden' to be :
a. Made of gold, consisting of gold.
So a coin made of gold may be either 'a gold coin' or 'a golden coin'. The OED, as far as I can see, makes no real distinction in concept.
The Ngram agrees with my own instinct and with my own usage of the two words, for 'gold coin' far surpasses 'golden coin' in usage, indicating to me that when English speakers wish to relay the idea of 'consists of gold' they will use the noun form.
The Ngram for 'wood/wooden door' however shows a completely different picture for here, 'wooden door' hugely outweighs 'wood door' in usage.
We use the adjectives 'golden' and 'wooden' to describe things that resemble the materials, either in appearance or in character - 'golden opportunities' and 'wooden behaviour' - but it seems we English speakers are not consistent in our use of the nouns.
Best Answer
Words like state and say take two similar but not identical structures as their object:
They can take a quoted string, the words uttered: He said "I won't go". This is sometimes called "direct speech".
Or they can take a clause introduced by that. This is "reported speech", and pronouns are substituted, and the verb are backshifted: He said that he wouldn't go.
That can often be omitted in reported speech; but it can never be inserted in direct speech.