'A lady is never so well dressed as when you cannot remember what she wears.'
The moral subject of jewellery appropriate to wear during the day came up over and over again in nineteenth century books and publications aimed at teaching young women style and etiquette. Young women in Europe and America were expected to want to get married and then manage their husband's households, staying out of the public sphere. Young men were expected to want 'modest' (whatever that means) and quiet wives, someone who would be happy to stay home and raise their children. Most if not all etiquette and household management books used moral arguments against wearing large or 'showy' jewellery during the day, and many were aimed at the growing 'middle' class, people who were the first generation in their family to have a disposable income, and who were nervous of disposing of it incorrectly.
The new possibility for people to start with very little and make their fortunes, regardless of family or connections, was a massive social change from previous centuries. The aristocratic/wealthy classes of the eighteenth century had assumed that family, connections, property, and power all came together, and always would. The famous 'gilded age' and Louis 14th jewellery show off wealth and splendour on an enormous scale.
With 'new money' gaining access to property and therefore power, 'good society' (old money) retreated behind a wall of 'good taste', so that admiring or displaying wealth for wealth's sake became frowned on. Jewellery worn in the 1800s was supposed to be either inherited from past generations, or gifted from close family. It was also supposed to be an expression of the young woman's 'artistic' nature and good morals, - pieces were meant to be prized for their design and workmanship over the size or cost of the materials. Having said that, the materials were always to be of the best quality, never imitation gemstones or plated metal. Imitation jewellery was always said to be in bad taste, as it appeared to be falsely advertising wealth and status. The fact that a woman might wear gold plated pieces because they were very well designed, or because she didn't want to spend so much money on jewellery, doesn't seem to have been considered.
Two images of women wearing day jewellery, on the left, Judge Mary Margaret Bartelme wearing a cameo brooch, and on the right, 'The Children's Holiday: portrait of Mrs Thomas Fairbain and her children', by William Holman Hunt 1864-5, showing Mrs Fairbairn wearing a coral brooch and earring set.