A synthetic lace won't go mouldy, that's something that only affects natural materials. Petroleum based fibres do not offer anything to feed spores.
Mandy, as I see it, here are the possibilities:
- A different material was used in those affected portions of the lace and it has become discoloured over the years due to a chemical reaction as a result of poor storage (plastic) or age. Against this idea:
- the pink would be visible in the underneath as well, not just on top.
- it would be more even, not random as pattern weaves follow a pattern.
- pink is a very unusual colour to discolour. I've never heard of this happening.
- modern (post '70s) synthetic laces are generally all one material.
To test this idea, see if you can see the pink appearing in the same part of the pattern elsewhere on the dress. If there is a regularity, it suggests it is a possibility. You could also perform a burn test on a small clipping to confirm the fabric composition.
- The pink has been applied in the intervening years. Against this idea:
- The dress has been in storage, has not been worn.
- Why would anyone do such a thing?
- If they did, wouldn't they "paint" the bodice front rather than random areas on the back?
Mandy, my advice is to wear the dress as is. If you really want to remove the marks and don't mind potentially ruining the dress, you could wash in a colour run remover. I would do that first before trying Napisan (oxygen bleach) as I find the latter rarely works on colour run. Colour run remover removes dye that shouldn't be there, so if it has been applied or developed somehow since it was last worn, it should improve it.
Failing that, I would hand wash in mild detergent and warm water and if that doesn't work then I'd go for the run remover.
The reason I recommend the run remover first is that subsequent treatments can set the colour - if you've had it dry cleaned, it's possible this has already happened but it's worth a shot.
Good luck!