DOUBLET:
Doublets are made of two layers that are glued together:
A black backdrop that can be formed of brown ironstone, hard plastic, black potch (colorless opal), black industrial glass, or even vitrolite.
a narrow opal slice (normally crystal opal or white opal).
Opal in a doublet can range in thickness, but it is often thicker than opal in a triplet. If there is enough opal, the edges of the opal slice are typically smoothed off to create a cabochon (domed top).
When examining the side of the opal, doublets can typically be distinguished because the line between the colored opal and the black backing is precisely straight if the stone has been cemented together. This is necessary for the two layers to be adhered together. Even for an expert, it can be quite challenging to determine whether a doublet is a doublet or a solid opal when it is set into jewelry with the sides covered. Doublets look considerably more natural than triplets since the top of the stone is made entirely of opal, giving it the appearance of a black opal.
TRIPLET:
Three layers make up triplets;
an above-described black backing,
With a paper-thin opal slice in the center.
A dome-shaped cap made of clear glass, quartz, or plastic that is transparent. The clear capping gives the stone a lovely cabochon on top because the opal slice in a triplet is typically quite thin (paper-thin). The opal's color may be slightly enhanced by the clear capping while simultaneously being protected. There's usually a shadow casted by the dome that is apparent around the edges of the man made stone.
an above-described black backing,
With a paper-thin opal slice in the center.
A dome-shaped cap made of clear glass, quartz, or plastic that is transparent. The clear capping gives the stone a lovely cabochon on top because the opal slice in a triplet is typically quite thin (paper-thin). The opal's color may be slightly enhanced by the clear capping while simultaneously being protected. There's usually a shadow casted by the dome that is apparent around the edges of the man made stone.
A skilled individual can quickly recognize a triplet opal by its appearance since triplet opals have a clear non-opal capping on top. Triplets typically appear "glassy," and the light reflects from the top of the stone in a unique way. Both the side and the back of the stone can be examined to spot a straight line where all the layers converge. You are not looking at a solid stone if the back of the stone looks like black plastic. However, you should be aware that black potch, which is the same stone used to make the backing of a natural black opal, is also frequently used as a backing.