Flag Colors and Corrosive Dyes

Old Glory over Baltimore Harbor

Certain colors are new colors and some are old. What I mean by that is there is a wide range of colors and tones that are cheap and easy with synthetic dyes but more difficult and costly with natural or vegetal dyes. Think of flags, before WWI almost all flags were Red, White, and Blue. Why? Because these were the colorfast light stable colors.

As we can see in this 48 star American flag from WWI above;

And this Union Jack from British Empire. They, as do most old flags, rely on Red, White, and Blue.  White because they could use natural white of bleached white wool. The usual blue is Indigo a very stable dye that we know from Blue Jeans. The red is typically from Madder mordanted with Alum. However insect red is possible in flags as well but less common.
The key is that we had a limited pallet of stabile colors for flags and rugs. When we see orange, green, black and others we know it is more likely after 1920. Here we have a great example of new flags. These would not have been practical in 1915:

Post 1920 Synthetic Dyes

Here we have the program from the 'Football Association of the Irish Free State' defeating the Nazi German team at Dalymount Park in Dublin on October 17, 1936. The Irish Free State gained limited autonomy from the cruel heel of British oppression in 1922 when they adopted this flag. The Swastika flag was used from 1933 to 1945.

The Reyn Staffel Sauj Bulagh Rug Azarbayjan-e-Gharbi Province

Corrosive Dyes

We can see in the magnificent piece from Reyn Staffel above is corrosive dyes. The brown and black wears away leaving a sculpted look.

Black and Brown were possible earlier but they were considered the most difficult colors to achieve with natural dyes. It was also prone to fading.  Black was achieved by adding iron salts to the dye bath. The problem is that it becomes brittle and the wool wears away more quickly. When this happens we call it a Corrosive dye. Typically in Antique Rugs Surmey Blue is used in place of Black. Surmey is over dyed indigo repeating the vat dying process until it appears almost black.