Formally silver kanji were introduced on December 28, 1937 by Ministry of Finance Ordinance No. 60 that prohibited the use (as wartime austerity measure) of gold in inscriptions, trademarks, etc.
Excerpt from original ordinance.
"... may no longer be produced ...
4. Gold letters, gold silk...
dating japanese award
dating japanese medal case
dating japanese medals
dating japaneseorders
gold kanjiletteringon the japaneseordercases
golden vs. silverkanjioncase lid
japanese awards and decorations
japanese medal casejapanese medal case with golden inscription
japanese medal case with silver inscription
japaneseordercase with silver inscription
japaneseordercase with silverletteringsilverkanjiletteringonjapaneseordercase
time borders of silverkanjies