Vintage 101: iron mordant in vintage textiles

Further to my previous post about what sun damage can do to your vintage, today I’d like to enlighten you about iron mordant.

You’re probably thinking….iron mordant? What on earth is that? Well keep reading, and you won’t need to learn the hard way.

I love black floral fabrics – in 1983 I wore a mid ’40s black floral rayon dress and my mum told me that her mother had worn them when she was young. My grandmother died when I was a baby, and there’s not much I know about her, so her love for black florals became a way to connect with her, and I’ve loved them ever since. More recently, they’ve become an easy way to wean myself off my all-black Melbourne wardrobe and get back into colour again.

Over the years I’ve found a few that were suffering from a strange condition: first was the red/white/black floral I bought on ebay and was described as “excellent condition” but when I hand washed it, a whole lot of holes appeared along the shoulders….when I looked closely, it was clear that the holes corresponded with the parts of the print that were dyed black. It was like they had been expertly cut out, as the other colours were fine and intact.

I’ve had a few since then, and the effect baffled me: they couldn’t be worn, washed or sold because the holes weaken the fabric and also make it semi-sheer. I searched for information in books but I didn’t know what I was looking for and so it remained elusive.

Have a look at this dress….it’s a late ’30s black rayon floral with puffed sleeves.

On the surface it looks nice and strong, with beautiful vibrant colours. Here’s a close up of the fabric.

However when you look closely, especially around the bodice and the shoulders, you can see the black dye is eating away the fabric. See how some of the weft (left to right) threads are there, but the warp (up and down) threads have gone, leaving a blank space?

It almost looks nice, and part of the design until you consider that the fabric is being eaten and is now weaker for it. To get a better idea of how bad the damage is, I held it up against a light (the best way to find holes by the way).

Here’s the bodice, near the smocking and neckline.

What’s going on!?!

Thanks to a recent thread on the Vintage Fashion Guild’s forums, I discovered early fabrics were often dyed with mordants, and black especially used an iron mordant which we now know can deteriorate the fabric over the passage of many years. From the Victoria and Albert museum’s site:

Metal salts were used as a fixative (also called a mordant) and to chemically modify the colour of a natural dye. One such mordant was based on iron, which gave a rich dense black. Over time, the iron salts attack the fibres themselves, weakening them to such an extent that they eventually turn to dust…iron mordants are chemically bound to the textile fibres and cannot be removed.

So the damage will only get worse, especially if washed or exposed to the air or sun. What to do?

Firstly, be aware and check the fabric condition before you buy vintage clothing pre mid ’50s (when synthetic dyes became common). Holding a garment up to the light will easily reveal the truth, and this issue seems to affect the bodice and shoulders more than the rest – although I do have a late ’30s dressing robe that has it scattered throughout the skirt.

Secondly, if you do have something affected, or if you just love it so much that you’re prepared to live with it, know that you will need to strengthen the fabric if you want to wear it. The affected areas could be darned or patched, or you could sew the unaffected fabric together over the holes.

Another option could be to use an iron-on patch or vylene. I don’t usually recommend using adhesives like these as they reduce the value and authenticity, and have the potential to damage the fabric, but this is already a damaged fabric that has lost much of it’s value.

For this particular dress, as it only affects small areas I used a combination of darning and sewing together pieces to make it wearable. Prints are wonderful for hiding repairs. This is only a stop-gap though as the damage will continue and if you wish to keep wearing and washing it, more repairs will be needed.


  1. ~ * ♥ * ~

    Wow, I had no idea about that sort of thing! It certainly make me think twice about buying black vintage online where I couldn’t see those kinds of holes… Thanks for the information. 😀

    bonita of Depict This!
    ~ * ♥ * ~

  2. Oh yes!!! I’ve had the same thing happen to a vintage Hawaiian rayon!! I figured it must be something to do with the dyes as it was only the black areas that disintegrated! That’s so interesting to find out! Thank you!

    PS I patched it from underneath with bits from the selvedges and hem, but alas they later disintegrated in the black areas too!!

  3. Wow what an unusual dilemma! It’s kind of tragic that this happens but it’s amazing that the rest of the garment has held up over more than 70 years…whereas most modern clothes would barely make 5 years without falling apart at the seams.

  4. That’s very interesting Nicole, I will be on the lookout for this and I think I probably have come across this before but not understood what was going on. I have in the past made a very strong black dye using leaves of red flowering gum and a nail as the iron mordant…I can’t remember what I used it on but it would only have been cotton or wool. I’ll keep this in mind if I do that dye again!

  5. Great and informative post. I too adore black floral dresses and collect them all the time. Though I haven’t run into this issue yet, from now on I’ll know to be more careful when considering earlier ones, no matter how much I love the print!

  6. I have an Amish patchwork quilt (a fabulous Lone Star pattern in navy, maroon, green, cream and grey), made in the late 1980s, in Pensylvania. In the last 10 years, while every other patch is in excellent condition, all the dark grey pieces have disintegrated…I can only assume there was an iron mordant used in the dye for the grey fabric.

  7. Thanks for this. I have a few old embroideries from India where the black threads have turned to powder basically.
    All the other colors are fine in the same pieces.
    I also started noticed this on some items for sale and have been looking to see what the cause is.

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