ARKitでオブジェクトが黒くなってしまう

##困っていること
ARKitを用いてオブジェクトを表示させたいが、画像のように黒いオブジェクトが表示されてしまう。

##ソースコード

Swift
1import UIKit
2import ARKit
3import SceneKit
4class BasicsViewController: UIViewController{
5
6    
7    @IBOutlet weak var sceneView: ARSCNView!
8    
9    override func viewDidLoad() {
10        super.viewDidLoad()
11        sceneView.delegate = self
12        sceneView.showsStatistics = true
13    }
14    
15    override func viewWillAppear(_ animated: Bool) {
16        super.viewWillAppear(animated)
17        let configuration = ARWorldTrackingConfiguration()//設定をする
18        configuration.planeDetection = .horizontal//水平面を認識するように設定[.horizontal, .vertical]で両方
19        sceneView.session.run(configuration, options: [])
20    }
21    
22    override func viewWillDisappear(_ animated: Bool) {
23        super.viewWillDisappear(animated)
24        sceneView.session.pause()
25    }
26    
27    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
28        let ship = SCNScene(named: "art.scnassets/ship.scn")!
29        let shipNode = ship.rootNode.childNodes.first!
30        shipNode.scale = SCNVector3(0.2,0.2,0.2)
31        
32        guard let location = touches.first?.location(in: sceneView) else { return }
33        let pos: SCNVector3 = SCNVector3(location.x, location.y, 0.996)
34        let finalPosition = sceneView.unprojectPoint(pos)
35        shipNode.position = finalPosition
36        sceneView.scene.rootNode.addChildNode(shipNode)
37    }
38
39}
40
41extension BasicsViewController: ARSCNViewDelegate {
42    func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {
43        print("anchor added")
44        if anchor is ARPlaneAnchor {
45            print("this is ARPlaneAnchor")
46        }
47    }
48}