This guide is a follow-up to my first guide on opal valuation. This guide will examine several of the more advanced topics in determining the value of cut opal.  I have been cutting opal for about 20 years and made most of the mistakes along the way.

This guide is a bit lengthy, so feel free to get a cup of coffee before you dig in. I will try to make it an interesting an enjoyable read (and use lots of pictures :-) ).

The topics of this guide are:

• Opal fire patterns
• Opal consistency/directionality
• Opal cuts (good vs. bad)

At the outset, let me say that some of the opal attributes will be difficult, if not impossible, to see based upon a picture or two. Therefore it is very important that you deal with a reputable dealer who will accept stones back if they are materially misrepresented. It is always best to ask before you buy and hopefully you develop some new questions from this guide.

Opal fire patterns - The pattern of fire in an opal is an extremely important contributor to the overall value. Some patterns are considered much more valuable than others and some are quite rare. In general, opal patterns fall into the following catagories.

• Pinfire - The pattern of the fire appears in a large number of points in the stone. This pattern is particularly common in Coober Pedy opal and some of the created opal. In general, pinfire is considered less valuable than other color patterns.

 Pinfire

• Flashfire - The pattern of fire occurs in irregular splashes of color across the stone. No single splash of color covers more than 50% of the stone. This pattern is quite common in Mintube and Lightning Ridge opals.

 Flashfire

• Broad Flashfire - The pattern of fire occurs in large splashes across the stone or the entire surface.

 Broad Flashfire

• Harlequin - This is one of the most commonly misused terms on eBay. Harlequin is a rare pattern and should look like flagstones across the stone all touching one another.

 Harlequin

• Rare Patterns - There are a number of rare patterns that occur in opals, some examples follow:

    Ribbon Pattern

  Straw Pattern

 Chinese Writing Pattern

In general, opal valuation is reduced (all other factors being equal) for pinfire, neutrally weighted for flashfire, broad flashfire and increased for any rare patterns or flashfire that rolls across the stone. The list of rare patterns presented here is not exhaustive (there are patterns such as picture stones, mackerel sky, flame, and chatoyant opal). Chatoyant is quite interesting...I have a black opal that I cut that is chatoyant. The color rolls across the stone like a star sapphire. Very rare! That one is staying in my collection. :-)

Opal Consistency and Directionality - Opal consistency refers to the uniformness of pattern, brightness or coloration in a stone. Any dull spots or pattern distractions significantly reduce the value of the stone. Directionality refers to whether the brightness of a stone varies significantly based upon the direction of viewing. This is a real tricky one to determine on ebay unless the seller provides pictures from multiple angles or an mpeg. When I list a stone, I usually indicate whether it is directional or not. Directionality tends to occur much more with broad flashfire and flashfire patterns. So, if you are buying a stone with this pattern (or in general) it is a good idea to ask whether the stone has any directionality. Significant directionality greatly reduces the value of a stone.

Opal Cut - There are well cut opals and poorly cut opals. Unfortunately, on eBay it is very difficult to tell the difference without examining the stone or asking. I will give you some general guidelines.

Opals are typically cut as cabachons, the shape of the opal may either be freeform or calibrated. A calibrated stone is oval, round, pear, square or triangular and of standard size (ex 8x6, 12x10). The advantage of a calibrated stone is that it will fit in a standard jewelry setting that is much less expensive than a custom setting. In addition, you typically lose more material cutting to a standard size. Freeform opals are of varying shape and size and typically require custom settings. Personally, I like freeform opals much more than calibrated, but calibrated stones tend to be more highly valued (per carat).

A well cut opal should not be too thin or too thick. In addition, it should have enough thickness on the edges to avoid potential cracking during setting. The dome of the stone can be high, medium or low. In all cases (except boulder opal or carved opal) the dome should be regular and not misshapen. A properly cut opal should have the back edges beveled. If it does not, the risk of cracking the stone when setting is very high. Always make sure that the back edges are beveled.

An excessively fat stone provides carat weight that is not necessarily valuable. In some cases, cutters will cut a stone with a convex belly to increase the carat weight. This is quite often done with Lightning Ridge black opals. The stone can be adjusted to compensate for this in valuation. In addition, stones that are too thin are fragile. The following is a guideline for thickness and weight for a few calibrated oval sizes:

18 mm x 13 mm

• weight range (5.5 ct to 9.5 ct)
• thickness range (4 mm to 7 mm)

16 mm x 12 mm

• weight range (4 ct to 7.5 ct)
• thickness range (3 ct to 5 ct)

12 mm x 10 mm

• weight range (2.5 ct to 4 ct)
• thickness range (2 mm to 4.75 mm)

All stones should have a good polish and appear glassy to the eye. They should be able to reflect the pattern of a lightbulb clearly on the surface of the stone. It is permissable to show some slight scratching under a loop, but they should always be eye clean.

Inclusions significantly reduce the value of an opal. Some opals (such as boulder) tend to generally show inclusions and that is accepted. In general, you should devalue an included opal significantly. Inclusions are typically potch or sand. Note that inclusions on the back of a stone do not change the value of the stone. In general, the back of an opal is immaterial to its worth (unless you can see it through the top surface).

A cracked or crazed stone has no value for jewelry. A cracked or crazed stone will break and/or desintigrate in jewelry. You might buy a cracked or crazed stone as a specimen, but never ever ever for jewelry.

Conclusion - Ok...you did well to make it through this guide. Hopefully, you have a whole new list of questions to ask when you buy finished opal on eBay. I hope you found this guide interesting and informative, if so, a positive vote is appreciated.