Affinity Photo gradient map with a transparent background?

[RoyalCaster]

I have a project in Affinity Photo where an electric guitar is on fire. I first created the flames in white with a special brush and then colored them with a gradient map.

Since this is a t-shirt design, the print shop logically needs it without a black background. However, if I remove this, the gradient map does not produce the black-red-yellow-white gradient that I would like for the flames, but a continuous, disgusting and bright yellow.

I conclude that the black background plays a role in the creation of the flames and I would like to know if you can think of any method or way of exporting the image as described.

I uploaded the project file and an image of the disgusting yellow flame I want to prevent.

Thanks in advance to all respondents :)

Mazze_Shirt.afphoto

[firstdefence]

All the black is doing is filling any translucent pixels black creating the contrast and enabling the flame form to be easily seen. Obviously if this is printed onto a black T-shirt the flames should show pretty much as they do now but this wouldn’t work well on a coloured T-shirt.

I think you need to add black/greyscale flames for the coloured T-shirts.

[firstdefence]

I’ve created some flames from a app I have called Flame Painter, it’s off the chart fun to use and the effects it can create are sublime.

This is your edited file with the flame painter flames included in two layer, the one shown here is the less hot lol! 

Had to zip it as I was getting the -200 upload error: Mazze_Shirt Flame Painter flames.afphoto.zip

[Lisbon]

Hi RoyalCaster!

A) With layer "Flammen" selected, go to channels panel, and "Create Greyscale Layer" from "Flammen Alpha"
At this point you will have a new layer.
B) Convert the new layer to a mask (Layer > Rasterise to mask)
C) Snap the new mask to bottom layer (Black background) and move both to group named "Original"
(By moving the black background to group the flames become more intense - don't ask me why)

End result...

[RoyalCaster]

Wow guys thank you so much... I did not exspect to get an answer the same day, but that really speaks for the forum.

Using a blackscaled copy of the flames perfectly worked out for me here! I have been working with Photoshop for years and recently switched to Affinity, but I never counquered a situation like this.

So both of you, thank you for your time and efforts and have a nice day