object/spring/back matches the site

public static HumanMadeObject Spring_Back()
{
    var springBack = new HumanMadeObject()
        .WithContext()
        .WithId("https://linked.art/example/object/spring/back")
        .WithLabel("Back of Spring by Manet")
        .WithClassifiedAs(Aat.Back, Aat.PartType);

    springBack.ReferredToBy = [
        new LinguisticObject()
            .WithClassifiedAs(Aat.InscriptionStatement, Aat.Statement)
            .WithContent("11505F")
    ];

    springBack.PartOf = [
        new HumanMadeObject()
            .WithId("https://linked.art/example/object/spring")
            .WithLabel("Jeanne (Spring) by Manet")
    ];

    return springBack;
}

• Metatype classification The second argument classifies the first, not the object: WithClassifiedAs(Aat.Description, Aat.Statement) says this is a Description, and Description is a kind of Statement. The Plain C# form shows the nesting.

var humanMadeObject = new HumanMadeObject
{
    Context = ["https://linked.art/ns/v1/linked-art.json"],
    Id = "https://linked.art/example/object/spring/back",
    Label = "Back of Spring by Manet",
    ClassifiedAs =
    [
        new Type("http://vocab.getty.edu/aat/300190692", "Back Part")
        {
            ClassifiedAs = [Aat.PartType],
        },
    ],
    ReferredToBy =
    [
        new LinguisticObject
        {
            Content = "11505F",
            ClassifiedAs =
            [
                new Type("http://vocab.getty.edu/aat/300435414", "Inscription")
                {
                    ClassifiedAs = [Aat.Statement],
                },
            ],
        },
    ],
    PartOf =
    [
        new HumanMadeObject
        {
            Id = "https://linked.art/example/object/spring",
            Label = "Jeanne (Spring) by Manet",
        },
    ],
};

Generated from the object the example builds: every property that is set, as object initialisers, with the vocabulary constants where a term is in the registry. The fluent helpers are a convenience, not a requirement; this form and the one as written produce the same JSON.