Thanks for the response.
I did not state that all Union flags were silk; what I did state that all of the flags made for units by the depots via their contractors were silk. Larger flags for posts, garrisons, etc. were not silk but wool bunting and these too came through the depots. These flags were going to spend a lot more time in the breeze and had to be much stronger so woll bunting was used. The wool flags made for company level and some early war regimental level flags were not made by depots for the most part. Most of them were locally made inclusing by women with connections to the unit. This is because the depot system was not yet ramped up (same for the Confederates). Hence the flags you mentioned that you saw. That must have been really neat to see!
I have done extensive research on Civil War flags for almost 20 years and when I lived in Ohio did a lot of work on the Cincinnati Depot which used not only two local flag makers (John Shillito & Co. and Longley & Brother) but also flag makers from the East. Some flags made for the Cincy Depot for distribution to western Union regiments were made through the Philadelphia Depot (via Horstmann's or Evans & Hassell) or the New York Depot (Alexander Brandon and others). It came down to who could supply the flags at the time of their need and if the local flag makers could not do it then the contracts were let to other sources. Hundreds upon hundreds of flags were made - many of which remained in depots after the war to be sent to the depot in Jeffersonville, IN for storage, sale and destruction in the 1880's. YOu could actually petition the War Department to buy Union flags in the 1880's and many were sold. Some were given to GAR halls while others were sent to forts, COngress and other places.
I was recently in the National Archives in DC and spent four days doing nothing but Union flag contracts research for the book I am doing on Tennessee's Civil War flags (we had a number of Union regiments here). I went through a lot of Union QM contract books and took copious notes on what depot ordered flags and from where. I will be back there in two weeks to complete that with one other contract source that I was told about from a fellow researcher that I was not aware of in June. These detailed contracts by depot QM officer to the flag maker and it was amazing to see how many flags were not made in Cincy for the Cincy Depot. It also seems that Longley & Brother made more flags than Shillito did.
The Cincy Depot started advertising in the area newspapers in early 1862 for contracts for a number of things including flags. This included Nashville, TN after that city fell in early 1862 by the way. It was through these ads that contractors got depot work and the depot was up and running by the Spring of 1862. QM officers at the regimental level then sent in requisitions (Form 40) to their brigade QM oficers which then went all the way up to theater QM officers which then sent them to the proper depot for filling. Supplies were distributed in a reverse manner back to the regiment. It was the depot QM officer in charge of whatever item was needed who let the contracts to makers no matter where they were. I will be detailing the operations of the Nashville QM Depot which was a sub-depot of the Cincy Depot in the book I am doing.
If you look at the regimental flags made by depots in the Time-Life book I cited you will see that all of them are silk. Regimental colors were specified to be silk ever since the Revolutionary War and remained so well after the Civil War even when the mid-1880's flag regulations shrank the overall size of colors to smaller levels. Modern materials can replicate that pretty well as I am sure you know.
Most units got their flags through the QM depot system as the army was standardizing their purchasing to make it easier to account for. Some units could, and did, order flags on their own typically with funds raised for that purpose, but this becomes less and less likely as the war goes on. SOme special presentation flags were ordered, like from Tiffany's in New York, but these were exceptions and not the rule. The demand for everything was simply too great and the depot systems, north and south, were set up to deal with massive supply problems. There were a number of early war flags that were made by local flag makers as well for units that raised money to pay for them. Longley & Broterh did a few flags like this for some Ohio units based on period newspaper reports I found over the years.
But the vast majority of Union unit colors came through the depots, paid for by the US government (some states like PA paid for flags for their regiments) and the vast majority of those flags were, indeed silk. The contract books I worked with in June had some of the dollar amounts for these flags and the bills were paid for by the US government and taxpayers. Each maker had to post bonds by the way before contracts could be let to them.
I have seen hundreds of Union unit flags over the years and at least 90 plus per cent of them are silk flags. I used to work for the Save the Ohio Flags Committee when I lived there and am very familiar with that collection, but I have also seen the flags in Iowa, Michigan, Illinois, Pennsylvania, Indiana and Kentucky (some of whose flags were made by Louisville flag maker Hugh Wilkins) and the vast majority of the regimental/National flags are silk.
I admire anyone that can sew anything much less flags. I cannot draw stick people.