Hello everyone, I thought I’d post this here even though it’s not really a question. It was however extremely helpful to me as someone who makes all my own alloys and will be helpful to others who do the same (such as Austin The Jewellery guy)
I found a fascinating research paper on karat metallurgy. It outlined how gold alloys May be classified by two parameters, gold purity and the ratio of silver in the master alloy. For 10-14 karat golds it classified them into three types, type one alloys were soft easily worked and non age harden-able, type two were tougher but still soft and age harden-able and type three were hard and not very ductile. Type one alloys had from 0-10% silver or 90-100% silver. Type two had 10-25% silver or 75-90% silver and type three was in the middle. This explains the use of zinc which has a softening effect by allowing higher copper content and less silver pushing yellow alloys into the type one or two range rather than three which is especially important at 10k. Not to mention that in low karats zinc additions improve colour.
For 18K the higher gold content means alloys that would fall into the type three range work like type two 14K alloys. At 22K all values are easily worked.