3D stamps are actually inverse soap stamps on a special curved base that imprints into the soap. But take a step back and look into the details of an inverse soap stamp.
Inverse = negative imprint = we imprint something that surrounds the outline of the design. Pff, this is way too much, isn't it? :-)
Look at the picture below and then I keep explaining...
At this point, guess which one is the normal stamp and which one is the inverse?
Ok, so I start with the normal stamp. Once we have a design available, we go along the outline of it, there are many different software out in the market. We trace the outline either automatically or simply re draw the design using arc-s and lines, splines and other primitives. This is quite simple. Let's take a look at the normal image below.
On the left side is the logo of a charity bid group and the right side is the normal soap stamp. Some things do not look good in real soap so the line strength can differ, but the design itself is simply the outline of the picture. As described above, there are numerous ways to achieve this. The more advanced the soap maker is the more "useful" differences can be applied to the digital design resulting in a better working stamp still representing the original image. This should always be a negotiation in between the soap stamp maker and the customer / logo owner.
Inverse verison of the design.
How can you recognise it?
As you may see everything except the design is imprinted. Everything in between the design elements. But what is going on with the outer circle? Well, it needed an extra line around that originally wasn't part of the image! I added it to add an external border around.
If still confused, see the digital representation of this:
Left: normal Middle: original graphics Right: inverse
That's all folks! :-) Hope by now you have a sort of understanding what the difference is between a normal soap stamp and an iverse soap stamp. A £d stamp is an inverse soap stamp, but the inverse design is inerpreted into a curved surface. ;-)
Finally here is a lovely short video