How can I reliably turn a shop-bought cake purple?

[Frankie789]

I’m wanting to make a shop bought cake that’s one of those DIY / Decorate yourself purple, how can I do it? Would an edible glitter spray work? If so any recommendations? I have one chance to do it so needs to be relatively reliable though not overly fussed if it’s patchy to be honest.

So is it iced?

Show the cake, or link to site you bought it?

If not iced, dye some white icing purple, and ice it.

If already iced, what type of icing is it?

I haven’t bought it yet but was thinking of one these that are pre iced - https://www.sainsburys.co.uk/gol-ui/product/sainsburys-birthday-celebration-decorate-your-own-cake-905g-serves-14

you can get one from M&S but that looks like it’s covered in buttercream which I’m guessing is more difficult to colour?

https://www.marksandspencer.com/food/decorate-your-own-vanilla-cake/p/fdp61218982

it’s for a kids party so I can add a topper that’s printed

You can buy edible spray paint for cakes.

The Craft Cake Company:

ShimmerDeluxe® Edible Metallic Spray 100ml – Professional Food Colouring & Shimmer Finish https://share.google/2IlBRzCFBty36EsCy

Bit pricey at about £12 but Amazon doesn't seem to have purple. Green or pink, yes but not purple.

Or this edible purple cake paint from Vanilla Valley, costs a bit less than a fiver and is on sale, as luck would have it:

Colour Mill - Purple - Matte Paint 20ml https://share.google/guDz8d3voRijIyNET

I'm intrigued though. Is it a Rapunzel from Tangled cake?

Like previous poster said, edible spray paint on this one.

Id probably make some purple fondant, peel off the existing fondant and slap.it on

You either to spray paint onto white fondant or buy a plain sponge and colour your own fondant then ice the cake with it. Purple food coloring also has a risk of looking a bit grey if you don’t buy a really good one.

How about tying a purple ribbon around it?

It’s buttercream on it right now.

It’s. Buttercream on there right now. Only thing you can do is spray it. Even a paint will likely start ruining the buttercream.

You can buy purple fondant icing and plain sponge cakes from Amazon or big branches of Tesco or Sainsbury

I think you could roll out some purple fondant icing, cut a disc and lay it on top of the buttercream, and do the same around the sides with a long strip of purple icing. Use the buttercream as adherent. Then cover the join with small decorations all around the edges

The first one has white icing on it. The second one has buttercream

Ah ok I only saw the buttercream one. My bad

Who is it for? Can you add purple fondant flowers, or a ribbon? Or make a marbled effect?

Mixing violet or red and blue with buttercream could work. At least you can see it before you put it on the cake.

I would order a buttercream cake, buy some pre-coloured fondant icing (Renshaw does a purple option), roll out and drape over the top of the buttercream. You'll likely need to warm a knife to just above room temperature and skim the very top of the buttercream with it so that the icing sticks. I wouldn't mess around with food colouring (purple is very difficult to DIY).

That won’t work very well for someone who’s not familiar with colouring buttercream, especially if they buy the wrong type of colourings. You need to use an oil based purple (definitely not a mix of red and blue, that will end up maroon) and for a deep colour use the microwave/immersion blender methods, otherwise you’ll end up with a horrid wishy washy mauve colour. You also need to make sure it’s the right consistency to spread and scrape it so it’s a nice flat covering.

I’m presuming if OP had a turntable, the right tools for frosting a cake and a vague idea of how to do it well she’d be baking her own cake. For a newbie I would recommend either purple fondant, which I’d put on top of whatever icing is already on there, don’t try to take off any existing white fondant. You may need to slightly dampen it for the new layer of fondant to stick. Watch a YouTube video for hints to do this part well.

Getting a nice smooth finish with fondant on a round cake isn’t easy, so painting the existing white fondant is probably the best bet for a neat finish, but again, you only get one chance to get it right - If you try to go over the paint again you’ll take it all off. Ask me how I know?! So I think I’d go for the edible paint linked above, or a petal dust mixed with a splash of vodka to make your own paint, but then you need to have enough to paint the whole thing so it doesn’t end up patchy. Sponging it on with a soft round sponge might work as long as you only go over each area once, as the icing will get sticky as soon as it’s wet from the paint.

If you are putting on a topper, id go for purple ribbon roubd the side and topper on top.

You can buy purple fondant icing - renshaw makes ready to roll purple fondant icing - for an eight inch cake, you’d need two packets. If I were doing it, I’d get an extra packet just in case!
I’d buy the buttercream cake, and put the fondant on top of the buttercream. You might need to use some sieved apricot jam - if it’s too thick, let it down with a little hot water - just heat the jam in a saucepan and add a little water as necessary - and brush it on with a pastry brush to get the fondant to stick. Just roll out the icing (you can use icing sugar to stop it from sticking to the side - don’t use cornflour for a dark colour) and then use a rolling pin to drape it over the cake like a tablecloth, and then smooth down. Put a little icing sugar on your hands to rub it smooth. If you have a friend who has done it before, then enlist their help!

If you dont think you can get it looking perfect then try the limewash effect which could hide some flaws. https://www.instagram.com/reels/DU927fGkhXb/

Getting a purple that looks even remotely good on fondant or buttercream like that will be incredibly difficult. Unless you have a spray gun it will look grey and patchy. You would be much better off not messing with the icing that's already on there but doubling down on purple additions - ribbon, fondant shapes stuck on, purple accessories or candles etc. I've made lots of cakes, including multi tier wedding cakes, and I wouldn't even attempt colouring icing like that

I’d buy the purple fondant icing and use it to make some decorations on the cake. Add a purple ribbon round it.