Pre-washing...Colour catchers.
 

I am making a black and white quilt.

This is a picture of the second set of colour catchers that I put through with my black fabrics.

Am I glad I pre-wash? You betcha because some of that grey would have ended up on my white the first time around.

Watson

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Indeed!! ...

Now, settle down those dyes now with a Retayne treatment.

How do you do a Retayne treatment? Throw the fabric/quilt in the washer with a 1/2 cup of Retayne and wash as usual?

How do you know how much Retayne to use?
I have about 10 yards of black fabric.

Watson

JaneQuilter and Watson ...
I'll answer both of you ....

Most LQS' sell it.
For Watson, I have never seen it at Len's, nor Fabricland, but not saying that other locations have it than where I have been. JaneQuilter, I'm not in the States, so don't know about Joanne's etc. I have seen here on the QB that some have ordered it online from Dharma Trading, USA based.

Here's a Dharma link that tells you more ...
https://www.dharmatrading.com/chemicals/retayne.html

I have always washed the fabric once with colour catchers.
If they come out coloured, I may wash and second time, but most times I go straight to Retayne.

I run hot water into my washing machine and add the Retayne. Let it Swish. Then add the fabric.
I usually toss in a colour catcher, just as a monitor, but have never had one come out coloured. Swish til all is soaked and submerged. Then I close the lid and let it sit. Usually hours rather than the 20 minutes they say. When I am ready, I finish the wash cycle ... and dry.

Until now, I have never heard the Synthropol recommendation but I don't see the need.
Actually I see it as countering what you want to do ... like it said, expect some fading.

Try this before you frustrate yourself with Retayne and more color catchers.

https://www.colorwaysbyvicki.com/sav...ing-quilt.html

Thanks, Peckish. I will try that, as I'm not sure I could get those other things around here.

Watson

There are directions on the bottle. It is figured by how many yards of fabric you are doing.

I used Retayne on 3 meters of beautiful, aqua blue, endlessly bleeding batik and was very happy with the results. I will say that I pre-rinse not wash with soap. I think that helps to minimize fading. I have also had good luck with a mixture of salt an vinegar. No real exact amounts--sort of a handful of salt (or epsom salts) and a good splash of vinegar in a sink of water.

I pre wash all of my fabrics with cold water tide and 3-4 color catchers.

I do the same with all finished quilts.

I use the color catchers until they fall apart.

This method has never failed me. I dry fabrics and quilts on regular heat.